You can manage the renewal status of your domain by login in to your portal and visiting Domain Names > My Domains

See this guide if you want to cancel a service such as website hosting, Google Workspace etc. 

NOTE: This is not instant and you will continue to get expiry reminders from us until the day of the expiry. This is because the domain is paid for until a particular date, and we are obliged to send you notices 90,60,30,7 and one day before expiry. 

The arrow on the right presents options to change the Auto Renewal Status.

Initially this will be displayed as Enabled

By selecting 'Disable Auto Renew', you can deactivate the auto-renew. 

You will now not receive an invoice to renew, and the domain will expire on it's expiry date at which point any services attached to it will also cease to work (e.g. websites and email).