Is it possible to renew your eTA?

No, it is not possible to renew an eTA. Your eTA is valid for five years or until your passport expires, whichever is the soonest. When your eTA expires, or you get a new passport, you will need to apply for a new eTA and complete the full application process again. You will also be required to pay for your application fee again.
When you get your eTA approved, it is linked to the passport using the details that you use in the application. Therefore, when your passport expires, your eTA is no longer valid and it cannot be transferred onto your new passport.
Before you plan any trip to Canada, you should check how long your passport has until it expires and you should also check whether your eTA is still valid. You can check the validity status of your eTA at any time, using the unique reference number that you were provided with when you submitted your application. It is a good idea to keep a record of your application and unique reference so that you have all of the details in case you travel to Canada again and want to check if your eTA is still valid.