If you follow the belt you will find a smaller (usually black) pulley that doesn't seem to hook to anything. It just idles in place when the belt spins. I have an */C engine so mine is in a little differnt location and such otherwise I could tell you the exact spot. It is probably on the belt between the Alt and the crank or water pump.
The top pic is what the pulley looks like, only it has a bolt going thru it. The pulley itself is actually spring loaded and offset from it'* connection to the engine block.
Find a socket or wrench that fits tightly over the bolt going thru it. Put the wrench on bolt so the handle points away from it'* mount. Then pull the socket away from the belt. This won't turn the bolt but will instead compress the spring giving slack to the belt. The pulley will physically be moving with the socket. Once you get the belt off you can let go of the socket (slowly) and let the pulley rest again until ready to put the belt back on.
I'll be hanging around a while if you got anymore questions or needs some more help.