Every time I use Photoshop I get a message that says my scratch disk is full.

Every time I use Photoshop I get a message that says my scratch disk is full. I have done all I know to do to free up storage on my MAC. I store almost everything on external hard drives. The suggestion online said to do something to the utility disk and I am afraid that I will delete something vital to the computer. My email seems to be attached to my computer and I do not not how to decouple that relationship.

[Re-Titled by Moderator]