Could someone explain the rules to me on substituting for a DH?

At times I'd like to move the DH to a fielding position and bring in someone else to DH. Is there a way to do this? Is it allowed?

Can I do a double substitution for the DH and a fielding postion and then reverse the DH and fielding position in the order?

I seem to be unable to make any changes to the DH except to pinch hit for him.

Obviously I don't know AL baseball rules.

Thanks for the help.

DaveF