No. You cannot change your data plan while your current rental period is in progress.
Changing your plan during your rental
Once you have started using a data plan, it cannot be changed during that rental period.
Changing your plan when extending your rental
You can choose a different data plan when extending your rental period.
For example, you can use the 500 MB plan for your original rental period, then switch to the 1 GB plan for the extension period.