Cannot change reserved instance type even if same family

Hello.

I have a t3a.micro ec2 instance and would like to upgrade it to a t3a.small. I also have a reservation (Standard) for t3a.micro.

Before doing so, I checked the t3a.micro reserved instance, modified it, choosing t3a.small as the new type in the selection. But when doing so, this error appears:

The instance size footprint of the new configuration must match the footprint of the original configuration. Change the instance type or count so that the new footprint does not exceed the original footprint. Learn more.

Despite reading the Learn more, it's not clear what to do to upgrade the instance type of the RI.

As per AWS, changing the instance size within the family should be possible:

When your needs change, you can modify your Standard or Convertible Reserved Instances and continue to benefit from the billing benefit. You can modify attributes such as the Availability Zone, instance size (within the same instance family and generation), and scope of your Reserved Instance.

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ri-modifying.html

Could someone please clarify?