Map [landscape/size] changing

I made my own map that i upgrade lots of times. It's full of custom units and spells with something like a month work.

What i wanted to ask is how i can change my map.
I want to make the map bigger and totally change the landscape. But I don't know how. The only thing i know how to do is Create a new map and paste over al Triggers, Units, Structures, Heros, Spells and much more. But That Takes to long.

So can someone tell me how i can make my map Bigger and change the landscape without hurting the things? Can i Paste everything over all in one?

go to map size and camera bounds in WE and change map size from there

For the landscape, or tileset, as it's called, go to Advanced > Modify Tileset.

It says:

the full map size must be a multiple of 32 in both directions. Can't i make my map bigger then it already is?

Yes. You just have to make sure that - as the error says - the map size must be a multiple of 32...

256 * 256 is allowed. 248 * 256 is not.

Already got it. Thank you very much!