I'm unsure if your if your mobo can even handle a 550 and even if it could, there's no point having a decent gpu but horrible cpu, it's the same as buying really good tires for your car, but your car is garbage so even if it is good, it's too unbalanced.
With those specs you should just save up for a new custom computer. And also, considering how old those specs are, i doubt your psu can handle a 550ti, but then again ya never know.