what happens if I screw it.
You might have to buy a new motherboard.
Bios updates deal with issues that crop up during the life of the board.
You may or may not be experiencing those issues.
The release notes on each bios version since your's should tell you what was covered by each update. If any of those issues affect you, then you have a reason to update, if not, then there is no compelling reason to do it.
Bios updates involve a small risk that you will stuff the mainboard, that risk exists for everyone, no matter how experienced.

Mainboard: Asus P5K-Premium, CPU=Intel E6850 @ x8x450fsb 3.6ghz, RAM: 4gb PC8500 Team Dark, Video: NV8800GT, HDD: 2x1Tb Samsung F3 RAID-0 + 1Tb F3, PSU: Antec 550 Basiq, OS: Win7x64, Display: 24&