Hi Olga, it sounds like you are using version 1.0 currently, which is the standard main released version.

But there is a beta (beta means an unfinished test version) release of version 2.0 available that you can download from here:
http://moi3d.com/beta.htm

One of the new functions for version 2.0 is a CPlane function that lets you change the orientation of the grid as I showed above.

There are also a whole bunch of other new things in the v2 beta as well, there is a full list of what is new so far here:
http://kyticka.webzdarma.cz/3d/moi/doc/V2releasenotes.html

- Michael