Reborn my PC

1st. Bought it in July 2011, came with almighty Windows 7 and later i decided to buy Windows 8 online (means i don't have a CD), updated to .1 and here i am.

This may be the easiest thing on the history of the easy things but i still don't know how to do it ("safely")

My PC is going through the fase where it gets slow opening things, i gave up on using Chrome since it is as slow as brazilians building olympic stadiums.

I just kind of wanted to make a big refresh but i don't want to go back to Windows 7, so, is there any way of doing this?