So my pc is 15 years old and i wanna upgrade it with 300$

You should add 4GB RAM ($25-50) and buy like a GTX 1050ti (About $200).
And don't know what you currently have for a processorr, but I guess if the processeor is also 15 years old, you schould buy something like a i3 oder i5, if you can afford more than $300.

Hope your thread wasn't a troll.