If you're going to upgrade, I would just build an entirely new rig.
Components are poor performance by today's standards, and the APU will struggle with anything above a 750ti, bottlenecking as a result.
Wait until you have a big enough budget, and post a thread here.
You'll likely need a clean install of windows if you do, as there will be a one time install on that prebuilt.
Windows copies are non-transferable across motherboards unless you do a fresh install, or have a reusable full copy of windows on hand with which you can migrate your OS.
You'd want a budget of about 700 pounds for a good midrange/value gaming PC.