How to upgrade a dell optiplex 760

hi i recently bought my new dell but it isn't as fast as id like. It was refurbished (bought from new egg) it was a good price and i kind of fell in love with it. id rather upgrade before dumping it but i also don't have a million dollars. My specs i suppose you'd call them are as follows: Dual core 3.00 ghz, 8gb of ram, 1tb of space, gpu Ati radeon HD 5450, 64 bit amd. Id assume it'd work for gaming and streaming but i cant figure out if just need a new graphics card or should i look at anything else. I'm new to this but I'm good with my hands and google has all the technical info I'm just looking for an opinion please and thank you. Any and all advice is appreciated. Please no just get rid of it comments unless there is no saving grace. Thank you again.