I'm trying to wire a new thermostat to my ancient heatpump but I'm not sure where the wires go exactly since the old coding is so different than the new new coding.

Old coding:
Wire color - location - my guess to new location
Green - G - G
Red - R - Rh
Brown - B - W/B
Yellow - Y - Y/O
Blue - X -??
White - W2 and E -??

please, someone help me!

Can`t help without knowing more info,, what brand hp,, what model number,, name of new tstat and model number,, and don`t take off the old stat till you get more info given to you,, you will need to tag or lable each wire as its removed,, color verses what post it came from

A lot more info will help. Is this an older rheem heat pump system your trying two rewire a stat for?