Hi, @Taka Thanks for the question and using the MS Q&A platform
If I understand correctly your max storage size has reached 14TB and you want to what are the options to reduce it.
The first check is if the data available is really required and claim back for a free space
Try to understand how this 14TB is distributed that can give more ideas and help to clear
Turning on Auto grow is a good choice however this will also fail if it goes beyond the max space available.
Please let me know if you are looking for any additional information.