I download my transactions from bank of america and I get 2 records for each one. Really don't know what to do.

Assuming you are not updating the account directly, can you try a different file format? I have seen this problem with some OFX files but never took the time to try to understand what the problem was.

How do i use a different format except for ofx? what format? Thanks.

This sucks. I really like the layout of this program. One of my accounts from the same bank doesn't have duplicates. This duplicate thing is really annoying.

You can file a bug for this. The best is to shorten the file to a single transaction, giving two in the ledger. A temporary solution could be to transform the input with a script prior to import.
Other formats would be QFX (Quicken Financial Exchange) or CSV (Comma Separated Values). Sometimes you still see QIF also. Most banks offer a choice.