OK, I can't find any reviews on your PSU, but thats not the greatest make in the world, and at around £20-£25 retail it doesn't inspire me to be honest.
You need to get out of your head that its all about how many watts PSU's have - its more down to how it can deliver the power in a stable and reliable fashion.
For example, a good quality make 400W PSU is likely to power a system more stably than a generic 600W piece of junk.
The bottom line is, try your current PSU and see how it performs - it won't damage anything, things just won't work properly if it isn't up to the job, or starts to fail - then go get a 500W PSU from a good make such as Corsair, Enermax, Seasonic, OCZ etc
I can highly recommend the Corsair HX520