Yep a 460w PSU is fine.
It's a pretty straightforward job really. Safety first though, make sure you unplug it from the power before working inside the PC.
You just need a cross head screwdriver. Sometimes the PCIe latch (which is usually a little plastic clip at the front of x16 PCIe slots) can be awkward but make sure you don't force anything when removing the old card. It should ease out.
Be aware of static, which has the potential to damage components. Touch the bare metal on the PC case before handling any components to discharge static from your body. Handle the cards components as little as possible (picking them up by the bracket or edges of the PCB). If you have to put a card down somewhere while doing the upgrade, use the anti static bag the card is supplied in.
Finally, even though they are from the same manufacturer I would fully uninstall the AMD display driver before removing the HD 6450 and then re-install the AMD Catalyst driver when you fit the new card. Don't know if it's strictly necessary, but it's something I prefer to do.
Don't know if this is any help, but it shows how easy it is really.
Edited by jonuk76, 16 August 2014 - 09:13 PM.