You can visit your Subscriptions page and edit your plan, whether that is it upgrade, downgrade or cancel. If upgrading or downgrading, changes take effect immediately.
When you cancel your SoundCloud DJ subscription, you can continue to enjoy access to all the SoundCloud DJ features, for the time period you have paid for. Once that payment period has stopped, you will be downgraded to the free SoundCloud experience.
Still need help? File a ticket.