It's not possible to change the bwlimit of Proxmox storages via the Web-UI (at least in Proxmox 7.x).
To change the bwlimit you need to use the pvesm
command and specify the limit for the desired category.
For example to increase the bwlimit for migrations:
pvesm set $NAME_OF_STORAGE --bwlimit migration=$INTEGER_LIMIT
# example
pvesm set ssd --bwlimit migration=500000
These are the different categories:
- default
- clone
- migration
- move
- restore