From what I can tell on the HP website, & some of the comments in their support forums, you're in a weird situation. First, it looks like the laptop uses "switchable discreet" graphics: the Intel CPU has integrated Intel-based graphics for "low-end" use (desktop, non-video-intensive apps like MS Office, etc.) that uses the laptop's RAM, & a discreet ATI Mobility Radeon 5650 for "high-end" use (games, video rendering, etc.) with its own memory. Can't tell if it's using fixed or dynamic switching, but apparently the Catalyst Control Center settings will show it (fixed = the laptop automatically switches based on hard-coded presets; dynamic = the laptop switches based on the application being run, but you can specify for particular apps which GPU to use).
In any case, it appears that the discrete GPU is built into the motherboard, so you'd have to replace the motherboard completely. However, there's a chance that the motherboard might have space to add additional memory for the GPU; in the DV6-6000 series specs, they mention one of the Intel CPU/AMD GPU motherboards comes with 1 GB for the AMD GPU but can be increased to 2 GB.