WP Defender Recommended Fixes

Looking at the WP Defender/Hardening (Action Needed) it recommend I change my database prefix to something new. This seem it can be some gobbledy gook stuff. I assume any number of characters or any alpha or numeric I want to use?

I also know that this does not change the prefix of wp tables but I am not sure if defender also takes care of this or if I should maybe use another plugin like iThemes Security?

I have about 7 issues showing up in WP Defender of which 3 were automatically fixed and this is the first one that I have to manually fix.

I already backed up my database in phpMyAdmin