The battery in a 2014 GMC Terrain is under the hood, but don’t feel bad that you couldn’t find it. It’s actually tucked underneath the Electronic Control Unit (ECU) and isn’t easy to see without some serious fiddling around.
If you feel comfortable taking some parts off your vehicle to access the battery, then you can change it yourself. But if you’d rather leave it to the professionals, then you can take your Terrain to a mechanic or GMC dealership to have them change the battery for you.