You can cancel your STV Player+ subscription at any time, effective at the end of the subscription period.
If you have a promotional discount (for reduced pricing or free months), then cancelling will stop STV Player+ benefit at the end of the current subscription period (monthly or yearly or 7-day trial period if applicable) - this may be sooner than the original term of the offer.
If your promotional offer covers multiple months you may wish to wait until the final month of the offer has started before cancelling, this will ensure you get the full benefit from that offer.