Can't be sure, but it looks like maybe a 12/26 maybe? Swap it to a 6 or 7 speed with a 28 tooth gear, and go compact up front. You should have enough climbing gears to work with then - maybe.

Looks like maybe they are, but it's hard to tell. What did the seller tell you? If you have indexed 6 speed shifting, fooling with the rear will not be as easy as with friction, unless you can set the shifters to friction to allow them to cover 7 speeds.