Walterono,
American Megatrends is just the name/type of your motherboards bios, dozens of other manufactures use this brand of bios too.
What you need to know is:
What make, model and version your motherboard is.
This information is written on the motherboard somewhere, find it, write it down, go to the motherboards website, download the EXACT flash and utility for your motherboard, (similar won't do)
Download Read Me files and any precise information regarding bios flashing.
Follow the proceedure to the letter or if you aren't confident let someone with experience do it for you.
Note*
Incorrectly flashed bios kills motherboards.
Martin Replying helps further our knowledge, without comment leaves us wondering.