While the GPU in this model laptop is not PnP replaceable, there are users who report that the GPU can be upgraded through some pretty invasive and warranty voiding physical and BIOS modifications. See the article linked below.
G73jh 770m GPU upgrade success
This user indicates some improvements with gaming but it's not something I'd feel comfortable doing myself. However, if you've got the right equipment and the know-how to troubleshoot possible setbacks, then by all means.
