This computer has a 300w psu, so my main concern is if I add another 4gb ram stick + a radeon 7770 gpu, will the power supply be able to handle it? If it can handle it would it be able to handle an additional i5 2500k or do you recommend me buying a new psu. By the way, I'm not experienced in this field.
Thanks for the advice, but the problem I have with building a completely new build is the fact that I am 14 years old and only get about 25 quid a week (Paper round) plus the fact that my parents are refusing to give me any money for anything electronic wise. So would it be worth it to save up for a year? Then build a completely new computer. Can I also ask why modifying a hp pc is a pain in the ass?