If you're on one of our regular paid plans, you can upgrade anytime under your Billing-->Manage Subscription tab. The system will charge a prorated amount based on how much you paid already and how much time is left in your subscription (if you're on an annual plan).

To downgrade to a lower plan, submit a support ticket to contact@mobile-text-alerts.com letting us know which plan you'd like to switch to and we can get it switched over for your next billing cycle. (You can view the current plans here.)