Comparing specs indicates maybe a 25% improvement for the CPU, assuming it's compatible AND the BIOS supports its full rated frequency.
Again though, here's the Catch 22 with upgrading CPU's in the same gen:
a) If there's a big processing advantage odds are they won't be compatible (TDP and cooling).
b) When they ARE within the same TDP so possibly compatible, the performance advantage is minor so why spend a lot of money go upgrade?
*It's also advisable to state WHY YOU WANT TO UPGRADE. For example, upgrading the CPU by 25% wouldn't benefit many game much due to the graphics bottleneck, whereas upgrading the GPU (if possible) tends to benefit mainly games and specific GPU-accelerated hardware.
OTHER:
SSD's are a great idea for general boot/load times for making your laptop feel "snappier"; I've heard good reports about this Hybrid (SSHD) drive that is 1TB and costs about $120 (Boot files and other files are copied to the SSD portion):
http://us.ncix.com/products/?sku=80986
There are THREE main thicknesses for 2.5" drives now: 7mm, 9.5mm and 13mm (or close to it). I believe 9.5mm is the most common. Just a WARNING as the 500GB has a 7mm version. In case you weren't aware you can CLONE or do a System Backup/Restore to use a new drive.
You can even take the previous 2.5" drive (if no secondary drive slot), buy a 2.5" USB case and use it for backup (including). *Always, always have at least one BACKUP IMAGE of your Windows partition in case of drive failure or data corruption. Windows backup, Acronis True Image etc..
Great value!