Cant raise terrain beyond certain height

I have used sketchup to create a fbx file of a terrain imported from google maps. I have then imported this into Unity and given it the texture of the map. I want manually alter the height of this terrain but I seem to be hitting an invisible ceiling…like there is a big invisible box around the terrain Ive create. Any ideas how I can remove or increase the height on this invisible box?
(I am very new to unity)

Thanks

You can change terrain height. Go to the inspector of your terrain click the wheel symbol and change the terrain height. This the way I can think of.

Even if it allows you to make higher hills, it does not raise the limit. It just sclaes the terrain so you can make longer hills.

Note: Set height before you do anything on the terrain.[202941-terrain-ınspector.jpg|202941]

Setin before raise. Cheers!