SOLIDWORKS Design & Help

Created by Angel Ramirez on 9 March, 2018

How do I edit this part to 410mm x 410mm

Hello,
I am attempting to edit this build plate to 410mm square. However, I cannot seem to edit the dimensions. I don't understand why. Can someone look at the file and explain to why I cannot edit the dimensions or explain how I can?

I am still learning Solidworks and am fairly new.

Thank you