That depends on a few things. Is the pass only active or has the validity of the pass also started? If the validity hasn't started, then you need to deactivate the pass. If the validity has started, then you can't make an exchange.

If you have deactivated the pass and the conditions for your pass allows an exchange, then you can make an exchange. The conditions regarding refund and exchange for your pass should be visible in your Interrail/Eurail account and on the invoice.