i watched my friend build my computer, it didn't seem that hard...

although i went to put in a card reader by myself and it took me a very long time because i didn't know how to make a slot for it in the case....

you need a friend who will put the pieces for you together!
it's not too too hard trying to figure out what you need, given what you want to keep you just need a new processor, ram, motherboard, case (i'd assume if you have cd/dvd/blu ray drives you'd keep that, and the thing you use to connect to the internet, and the harddrive unless the motherboard wont accept whatever the harddrive uses to connect to the itself)

not sure what else you need...

you probably wouldn't need to go all over the place looking for the pieces either, just avoid the online only shops and ones that look like they'll just take your money and run

and if you can't find a friend who will piece the stuff together there's probably people on the internet who will tell you