Yes, you can upgrade or downgrade to a different plan at any time.

If you upgrade to a plan of the same billing interval (e.g. PAYG Monthly to Starter Monthly), your license costs will be pro-rata adjusted and shown on your next invoice. If you upgrade to a plan of a different billing interval (e.g. PAYG Monthly to Starter Annual), your license costs will be pro-rata adjusted and shown in a new invoice created at the time of the upgrade.

When you upgrade, you can enjoy the new higher Plays quota immediately. This is one way to reduce your cost if you have gone over quota towards the end of the month.

If you downgrade to a cheaper plan, the change will come into effect from your next invoice. Your Plays quota for the current invoice period will not be affected.