so if I have matter rearranger ring on a figure with '0' range, can I rearrange a square of terrain adjacent , or just the one he occupies? I would think any adjacent square, since 0 range is adjacent. hope I have been playing it correctly. thanks everyone!

This is incorrect. An Adjacent Square is 1 range away. 0 Range is the square you currently occupy.

If you have 0 Range you can only use the Matter Rearranger on the square you currently occupy.

Also, when asking a rules question please provide the text for the power/ability in question:

Matter Rearranger: When this character has no action tokens, give it a free action, and choose a square of blocking, hindering, water, or clear terrain within range and line of fire. You may replace that square with one of the other three types listed.