How to open remote cover to replace batteries?

There may be some tabs around the edges that you need to push in and pop the halves apart. I'm not familiar with the specific model. But that's how a lot of garage door openers are (which in the future it might help to specify that you're talking about a garage door opener... "remote" made me think of a television remote until I searched the model number).

Some others I've seen also use screws or even just a single screw. Those might need either a Philips head screw driver or a Torx head (Torx - Wikipedia, the free encyclopedia).