I assume this is a part of a condo, so make sure you own a unit in the building because most will not let you own a parking space if you don't own a unit.
Also, you will need to know if the parking space is secured as park of your friends mortgage. If it is, he will need to contact the mortgage company and make sure they will release their lien on that spot without your friend paying of the mortgage. He may have to pay part or all of the proceeds to his mortgage company to get them to release a lien.
Otherwise, it is a relatively straight forward transaction and you should be able to complete this with the assistance of a title company, but don't necessarily need the assistance of a Realtor.