If you can't afford to upgrade your entire computer system, then go to your motherboard's Support site and see what CPU's are compatible with your motherboard.
If your motherboard uses a AM3 socket and not a AM2+ socket, and your motherboard is one of the later models of AM3, it may support AM3+ processors like the AMD FX Series processors.
If you post your exact Motherboard Make & Model I can check to see if it has a CPU Compatibility list and BIOS versions needed to support the CPU that are listed.