where can I change the names of these menu items? I want to keep them in columns, only by changing the names.
The second question: how can I replace this illustration?
1/ Find out which HTML block is added to mega menu: Appearance > Menu > Enter menu item > check Description field http://prntscr.com/j17fim If you do not see the Description field, activate in the Screen options http://prntscr.com/j17g2x
2/ Navigate to HTML block, find id specified in the Description and edit.