Veiker, welcome to the forum.
Here is a guide that will help you with your choice of a second processor. As you will see in the Caution: section, the second processor should match the original exactly. Also, here is the Setup and Install - General section for the computer. This section has all of the information that will need to upgrade your computer.
Please click the Thumbs up + button if I have helped you and click Accept as Solution if your problem is solved.