Hello @rene-dhemant and welcome to the Cloudron forum
This question should be targeted at your hosting provider, and they should have a guide for that.
Example guide from some DigitalOcean: https://docs.digitalocean.com/products/volumes/how-to/increase-size/
WARNING
Always make sure you have a valid backup before doing anything like this.
To boil it down, it should be very simple.
ssh into your server
run the following command:resize2fs /dev/sda3
confirm the size of your partition with the following command:df -h /dev/sda3
But please check with your hosting provider if he offers a guide specific to their platform.
