In general, it's usually not really worth upgrading a CPU unless you're going to replace it with something that's, say, twice as fast. You might upgrade and find yourself in the same position as you're in now within a couple of months if you only upgrade a little.

Well anyway, assuming you want to upgrade, if you can give some information about your motherboard that would be a good start. Best of all is if you can give the make & model of your motherboard, but if you can't find that out then if you could find out what kind of chipset you have on the motherboard that would be useful, along with what kind of slot/socket the processor is sitting in. There was a period where CPUs were made into cartridges that fit into slots, instead of just large chips that fit into square sockets, so you need to know which it is to know what kind of processors will fit