Well, for starters I would have to strongly suggest that if you have *anything* important on the arry, you should have already made a backup.
As for taking care of the bad sectors; you should just be able to unmount (for safety) the filesystem(s) on the RAID5, then run a full fsck to pickup and remap any bad sectors.
If that doesn't work, then as long as you're sure which device is reporting the problem, you could rip it out of the RAID5, reformat it, then add it back. By "reformat" it, I specifically mean run mkfs on it, then do a full fsck on the disk (check the man page for the options you will need).
If you're new to Linux, then I'd like to pass on one major tip:
Read the "man" pages for the various commands you see used in your google results. Not every Linux distrbution behaves the *exact* same way (For example: Red Hat-based distros vs Debian-based ones).
One more thing; Grab O'reily's "Essential System Administration, Third Edition
", it'll give you a great start on some of the "Common Good Practise" things that make UNIX/Linux system administration really easy.
P.S: If this helps, click the "Thanks" button on the bottom-right of this post.