Can I upgrade my logic board?

James you currently have the most powerful model in this series of systems. So upgrading the logic board here is just not possible.

The best solution here to sell your current system and buy a newer model (new or used) that meets your needs.

Just so you know there are a few things you can do to improve your systems performance. Like upgrading the HD to a hybrid drive (SATA II 3.0 Gb/s) as well as up the memory to 6 GB. With these improvements you should be able to get another year or two more out of your system.