What is it about your current computer that makes you think it needs an upgrade? Is it rather sluggish?
For your purposes, there's actually no reason at all why you should need an upgrade - expect perhaps a bit of extra memory could help if you're creating large slideshows. If the computer has got slow, then it's probably clogged up with temporary files, redundant DLLs and all the general dross the Windows accumulates over time.
I should try a Spring clean, first of all. If you haven't already got it, download the free Ccleaner (click here), and run it to clean up your files and your registry. After that, run a defrag.
That should make a fair bit of difference, but if you want to take the clean-up to the ultimate, then a full reinstall of Windows would be best. Make sure, of course, that you save all your data to an external drive of some sort first.
To upgrade the RAM, go to Crucial's website and run their memory scanner (click here
). This will tell you exactly what memory modules to order. In their Support section you'll also find a video tutorial on how to install the modules. It's cheap and easy.