The only CPU's that fit in this motherboard are;
Intel Core 2 Quad (Y) Q9xxxx
Intel Core 2 Duo (W) E8xxx
Intel Core 2 Quad (K) up to Q6600
Core 2 Duo E6x00 (C) up to E6700
Core 2 Duo E4x00 (C) up to E4400
In that regard you need a new motherboard mate, the Motherboard and case are cheap components by comparison to what your quoting you need, you may aswell start from scratch if you want something half decent otherwise your throwing good money after bad by trying to upgrade that thing.
Like the above poster said. Pre-built branded machines are usually not worth upgrading, some of them use custom-designed power supplies, most of them have very limited upgrade options on CPU and GPU fronts, and it is usually a better idea to build a new rig from scratch. Then you can customize whatever you want.
If you have a budget in mind let us know and we will be able to put something together for you at your budget. Just need to know;
1. Your budget (jn USD roughly)
2. What you intend on using the PC for (Gaming ? Streaming ? Video Editing ?)
3. Do you have a monitor already or is that meant to fit in your budget ? If you have a monitor what is it (Resolution and Refresh Rate) ?
If you give us that information we can give you a system that we would build on that budget so you know you'll get the best bang for your buck !!!