lightsail SSD size back

I was using a $20 instance with Lightsail Since /dev/xvda1 has reached 100% usage (80GB/80GB) I created a new instance from the snapshot and created a $40 instance.

Immediately after creation, /dev/xvda1 was at 50% usage (80GB/160GB), When I checked half a day later, /dev/xvda1 was at 100% usage (80GB/80GB).

On the console it says "8 GB RAM, 2 vCPU, 160 GB SSD", It's definitely on the $40 plan.

Do you know why the trouble occurs? Also, please tell me how to solve it.