First of all, you have to get information about the mating season of bats and if there mating season is in progress then you have to get a bat removal permit for getting rid of bats in your garage.
However, there are many states in which there is no regulation of getting permit for removing the bats from your garage. So, check the regulations of your state before removing bats.
You should employ those methods that do not involve killing of bats as in many states it is against law and can cause you greater trouble.
You need to examine your garage during the daytime for getting an idea of the number of bats that are living in the garage. Look the holes in the garage which bats will use for mating. Also examine the holes from where the bats enter and leave the garage.
Now cover all holes from where bats enter into the garage. Leave just one exit from where they could escape when you start pushing them out.
Use plastic sheets to cover all holes the bats use for entering into the garage. Also examine and cover if there is any space left in the garage door.
Now wait until the night when bats fly out for food and then enter into the garage for checking out how many bats are still in the garage.
Go to the garage again at early morning to check how many bats have come back. You will notice that there will be a considerable decrease in the numbers. Many bats fail to find the hole that they have been using to enter into the garage because you have covered those holes with plastic sheets.
In a few days, you will notice that all bats are gone because usually bats use a specific hole for entering in a garage and use a different hole for exit. When you see that there are no more bats left in the garage, remove the plastic sheets and cover the holes with bricks or any other solid material.