Spellrank

Simple command based off the addon UpRank – Addons – World of Warcraft – AddonsWoW.

Just type /spellrank and it will replace all spells on your action bars with the highest rank available. 

Don’t use in combat. 
Has only been tried on a shaman lvl 40 ( does not change spells on the special totem bar for shamans ) and a lvl 50 warlock but worked flawlessly.

Related addons:

JSpecBar UIAutoHide WowInfo SpellBook Abridged for WoW Classic Ogrila stone for Dummies RepositionTopFrame Hide Micro Menu And Bag Bars MissingPower (How often you can cast an action)