On non-A/C cars the alt is on the top IIRC, so it's pretty easy. Put it in high and on full right lock. Throw a jack or axle stand under just in case it decides to drop

Remove the driver's side wheel arch liner. Clean up the adjuster screw (6mm allen screw) on the bottom of the tensioner pulley you have just revealed, and WD-40/plus gas it. Slacken the two allen screws clamping the adjuster - one below the pulley, one in the centre of the pulley - to get the center one, unclip the bottom hose and gently move it down - there might be a plastic clip in the center of the pulley - prise this out first. Make very sure you are using the right allen key, the screw is well cleaned out, and the key is bottomed in the hole - you do NOT want to round one of these out.... Screw in the adjuster to let off the belt tension, then remove the belt - noting the routing!! Now just remove and refit the alternator, refit the belt, tension it with bottom adjuster screw - reasonably tight on the main run - and then refit everything else.