the problem is that DDR2 ram cards are old and have been replaced by newer DDR3 and that's going to be replaced by DDR4, I'm not sure if it's worth upgrading DDR2 memory anymore because you have to pay so much to increase it. What's your whole PC spec or don't you know?
yeah in my opinion it's not worth upgrading that system, the parts are too outdated and so expensive whilst performing slowly. you'd be best putting that £80 into a new £300-400 system and hey you might be able to salvage some parts such as case/HDD.
here's a build it yourself PC, full system with a copy of windows for sub £400, if you want I can do a system for £350 as well (it'll be the same with a 500gb hard drive and a weaker graphics card most likely
What do yo use your PC for however sorry? that'll help me get a better idea of what you need and do you want to build the PC yourself or prefer a built one?
You will get better performance per £ by building it yourself.