A 14 mm (or possibly a 13 or 15 mm) socket should do the trick for removal. You won't be able to budge the crank arms after removal of these. For this you'll need a Crank puller. One aspect of this tool threads into the center of the crank arms (not the same spot as the fastener you just removed but right around there). Then a second bolt tool with a special head threads into the first part, pushes on the spindle of the bottom bracket which affects the movement of the crankarm off the spindle.
Here's a link to a Crank puller.
Here's a couple "for instance" chainsets that are around the level of your current one:
Shimano Tourney, SRAM
Should you choose to remove and change your bottom bracket, which the specs for your bike state is a Shimano cartridge-type BB-UN26, you will need a bottom-bracket tool.
Cartridge bottom brackets last a long time, so it's likely you don't necessarily have to change it as long a the spindle is in good shape and there doesn't appear to be any grinding or roughness when you spin the cranks (with the chain off is best as you get a better feel for the status of the bearings without the noise and vibration of the chain).
One aspect to think about, is if you choose to remove your old bottom bracket, that will open up your options as far as cranksets go. Now days, the bearings are external to the bottom bracket shell, are far lighter than cartridge bearing BB's, and the cranksets are two piece: the right arm with it's chainwheels also has a spindle attached which the left arm slips on to and connects the system together. While they sell and advise the use of special tools for these bottom brackets and an aspect of the crank, one can get by with more common tools used with good sense