Either is grammatically correct: eliding the to would be called ellipsis, and it is normal in English. The second to is redundant when considering the previously supplied grammatical context. Consider the following ellipsis:
Original: To change your preferences or to change your subscription list, click here.
Ellipsis: To change your preferences or your subscription list, click here.
Here, the second to change is redundant, and can grammatically be removed. You could also omit the second your:
Ellipsis: To change your preferences or subscription list, click here.
While either will (almost always) be acceptable, ellipsis is generally preferred because of efficiency.