I have a toshiba 15.6 inch laptop...?

for some reason my screen is very dim, and I can barely see what im doing on their. Also, it had microsoft 2007 loaded onto it, even though it's windows 7, how do I upgrade & sucessfully (I have tried before & it doesn't work) to microsoft 2010? I am willing to pay for it, I just don't know how to do that stuff.