Upgrading RAID Controller

Hello. I currently have an Adaptec 2420SA and want to upgrade to 2820SA. Currently have a (4) HD RAID 5 config with (4) 300GB maxtor sata drives. I am using this config as a server to back up files. I have OS installed on one of the drives in the RAID.

My question is if I upgrade to 2820SA card will I have to re-install OS and will I loose all my info that I currently have stored on the RAID???