How to change map size of an existing map?

[Gluttonous]

I know I have done this before, but cannot remember how for the life of me.

Scenario > Map Size and Camera Bounds is not letting me increase the size of my map.

And no, I'm not talking about increasing beyond 256x256. My map is currently 128x128 and needs to be increased.

 

[Juno**]

Scenario > Map Size and Camera Bounds

Try checking the Modify map bounds box then try it again..