How can i marge my fan pages

You cannot merge (that's the word you're looking for) your fan pages on Facebook. All you can do is close to two smaller ones and redirect your fans to the biggest of the three and hope they will choose to come over.

Most of them will not. It is not easy to get people to move over. And that is precisely why Facebook does not allow merging. They know people join one group but might not want to join another one, or might think better of it later.