How do i remove the rear wiper arm on a 2013 ford edge.

Grab arm twist back and forth more than you think you should. they are a compression fit with friction splines.

You can replace the arm assembly without removing that nut. I did it after I could not get the nut off and I did not want to break the glass. First remove the little cap on the left side of the arm assembly. It snaps off. Then, grab the arm assembly and blade in your right hand. Pull hard to the right and twist down. The arm and spring inside will come off. Put the spring inside the new arm. Hook the loose end of the spring over the short shaft under the nut. Pull the arm and blade assembly hard to the right again and the slotted end of the arm with reseat on that short shaft. You're done. From Rich.

I put the nut on so i wouldnt damage the top of the threads,used adjustible pliers from the base to the nut ,little pressure and wiggle it came off

Copied one suggestion of using the nut on top so as not to damage thread and used large adjustable grips and with a little pressure and worked all the way round a bit at a time and this then worked. Also used WD 40 to help