"How to delete a macro variable?"

Hi,

How do we delete a macro variable created in RM?

Also, once the run of a an XML file is complete, and if I create a loop to rerun the same again, the %{a} takes a contnued value and does not start from 1 for my new run of the XML file. How do i get the %{a} to take from 1 in the second loop of the XML run?

Thanks,
Shubha