The scheme defines the repeat pattern of the curtain wall.
The boundary line is most easily seen, and therefore editable, when only the scheme is set to be visible. It can be edited like any other polygon such as a fill, slab, roof etc. You adjust the edges when you see a mercedes shaped cursor.
If you want to set a specific height other than what you originally set when first creating the CW, then define a local origin alt/opt+shift from which when you adjust a boundary frame you can then enter the precise height.
HTH
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"