When logged into the site in the download center there is a link to reset your current activations on the right, here is a link to the page:
downloadcenter.php
You are ok to have it on both machines, this is why we allow for two activations. However if you have some recorded for one machine and need to manage the activations this is the way to do it. Once you have cleared the activations you will be able to activate the product with your valid serial number.