How to upgrade a prebuilt PC - what's worth it and what isn't

Prebuilts cut corners in predictable places. The case is cheap, the PSU is undersized, the RAM is running slower than it should, and there's probably a spinning hard drive somewhere doing nobody any favours. The good news is that most of these are fixable without touching the parts that actually matter.

Check what you're working with first

Before buying anything, find out exactly what's inside your machine. Download HWiNFO64 or Speccy and note your:

• CPU model and generation
• Motherboard manufacturer and model
• RAM speed, capacity, and number of slots used
• PSU wattage (may need to open the case - it's printed on a label on the unit itself)
• Storage type and available slots

The motherboard model is the most important. It determines what RAM speeds are supported, whether you have M.2 slots, and whether the CPU can be upgraded at all. Search the model number on the manufacturer's site and read the spec sheet.

Worth it: add an SSD if you're still on a hard drive

If your prebuilt shipped with a spinning hard drive as the boot drive, replacing it with an SSD is the single most impactful upgrade you can make. Boot times go from minutes to seconds. Applications open instantly. The system feels like a different machine.

A 500GB SATA SSD costs around £35-45. An NVMe M.2 SSD is faster still and costs similar - check your motherboard has an M.2 slot first. If you're replacing the boot drive you'll need to either reinstall Windows or clone the existing drive, but most SSD manufacturers include cloning software for free.

Worth it: upgrade your RAM

Prebuilts often ship with a single RAM stick rather than two. A single 8GB stick means you're missing out on dual-channel mode, which can improve performance by 10-20% in memory-sensitive tasks just by adding a matching second stick.

Also check whether XMP or EXPO is enabled in the BIOS. Many prebuilts ship with fast RAM running at its slow default speed because nobody bothered to turn the profile on. That's a free performance gain - see our guide on BIOS settings for gaming.

If you're on 8GB total and use your PC for gaming, upgrading to 16GB is worthwhile. Beyond 16GB the returns diminish for most people unless you're doing video editing, 3D work, or running virtual machines.

Worth it: upgrade the GPU

This is the highest-impact upgrade for gaming performance and usually the most expensive. Most prebuilts at mid-range price points come with a GPU that was chosen to hit a margin target, not to deliver the best gaming experience.

The catch is the PSU. Prebuilt power supplies are frequently underspecified - a machine that shipped with a GTX 1650 (which needs no external power) may have a 300W PSU that simply cannot run a modern mid-range card. Check the GPU's TDP and add your CPU's power draw, then compare that to your PSU's rated wattage. If it's marginal or over, the PSU needs to go in at the same time as the GPU.

Worth it: add case fans

Prebuilts often ship with one or two fans doing the absolute minimum. Adding intake fans at the front of the case and making sure there's exhaust at the rear drops temperatures across the board, which improves sustained performance and component longevity. Decent fans cost £8-15 each and the difference in airflow is significant.

Probably not worth it: upgrading the CPU on an older platform

If your prebuilt is more than four or five years old, the CPU upgrade path is likely limited or closed entirely. Even if a faster chip is available for your socket, you may be spending £100-150 on a CPU that's still paired with a slow hard drive, 8GB of RAM, and a weak PSU - and the overall improvement will be underwhelming.

In most cases, money spent on a CPU upgrade for an older prebuilt is better spent toward a full system replacement.

Probably not worth it: upgrading RAM beyond what the platform supports

Adding 32GB or 64GB of RAM to an older platform that's bottlenecked by its CPU or storage makes no measurable difference for most workloads. Prioritise the components that are actually limiting performance first.

What to watch out for with prebuilt cases

Some manufacturers - particularly at the budget end - use proprietary form factors for the motherboard, PSU, or both. This means standard ATX parts won't physically fit. Check before buying anything. If the PSU uses a non-standard connector layout, a standard replacement won't work without an adapter or a new motherboard.

This is more common with small form factor and all-in-one prebuilts than with standard tower cases, but it's worth confirming before you commit to an upgrade path.

When to send it in

If you're not comfortable opening the case, swapping a drive, or identifying whether your PSU has the right connectors for a new GPU, these are all jobs we can do quickly on the bench. It's also worth getting a second opinion before spending money on upgrades for an older system - sometimes the honest answer is that the money is better put toward a replacement, and we'd rather tell you that upfront than have you spend £150 on parts that don't move the needle.