Everytime, I change the size of the part; it moves upwards and always stays there. I tried changing the position when the size of the part changes but it didn't seem to work.
Make sure the part is anchored first of all, and instead of setting the position, set the CFrame, this ignores collisions and won't force the part to move up. To do this set the part's .CFrame
to CFrame.new(10,20,30)
(the numbers are just like Vector3 values). You can then explore CFrame further and learn how to rotate the part by reading through the wiki page I attached above, I can't explain how you do the rotations because it confuses me...
Hope this helps, if it does vote it up and accept it as the answer.