Yes, and most suppliers will even waive any exit fees your current tariff has if you choose to switch to another of their tariffs - though always check with your supplier first.
If you switch from one tariff to another with the same supplier, it’s usually a much quicker process. Some suppliers also backdate the switch to when you applied, meaning you’ll be charged the new rates from the date you requested the switch. So if your current tariff is cheaper than the new one, you may want to hold off until nearer the end of your deal to get the maximum benefit from your current tariff. However, as tariffs change daily, there’s no guarantee that if you wait the tariff will still be available.