Normally, I need to crush people's dreams about upgrading their laptop's video card because for the majority of them it simply cannot be done. Generally speaking video card upgrades are limited to more expensive laptops; like $1,700+.
However, in your case you can. The Y710 takes a MXM II (consider it a "slot type") video card. Here's a Mobility Radeon HD 3650 for $120:http://cgi.ebay.com/NEW-ATI-Mobility-Radeon-HD3650-MXM-II-VGA-Card-512MB-/200555172499?pt=PCC_Video_TV_Cards&hash=item2eb2051293
Word of warning, you will probably need to update the BIOS in order to use it. Lenovo's site should have it. Additionally, you also need to verify that the BIOS update will recognize the card. If you install a video card that the BIOS does not recognize, then your screen may simply be blank.