First, you must make the decision to keep these beneficial animals in your neighborhood, by installing a bat house or bat box.  You'll want to place it as close to the bat excluder as possible, for them to easily find it. 

This bat excluder comes with instructions...you will want to install it after the 2nd week of November, when all of the young bats are able to fly out of your building.  First, seal any exits or entries that the bats are not currently using, by watching them at dusk.  Next, place a bat excluder over the major exits, the bats will be able to exit, not enter, due to the slipery sides of the tube.  Finally, monitor the bat excluder, you should see fewer and fewer bats exit every night, if not, look for other exits and entry ways the bats may be using.  Finally, when you don't see any more bats exiting the building through the excluder, remove it and permanently seal the final exit with wood, caulk, steal or other permanent fix, not expandable insulation. 

Once the bats are gone, you may have the urge to immediately clean any guano, (bat droppings).  Please read carefully, as this can be dangerous.  You should wear protective equipment and use an industrial vacuum, not your regular carpet vacuum.  For protective gear, you will need a respirator and possibly a full body suit, which are both available at Grainger, or your nearest hardware store.  The other option is having a professionally trained expert coming to your house to do the cleaning, it may be expensive, but so will the protective equipment.