I did a little research for you, and, unfortunately, the only option you have is to send it in to HP to have them upgrade it.
This is the
thread I was looking at from the HP support forums. The last post says he was able to send his DV7 in and have it upgraded for $75.
Other than calling HP, and unless you just need a larger hard drive, upgrading a laptop is either impossible(parts not made/available) or it's more money/effort than it's worth.