Web Admin license does not allow managing Subscription limits in administration panel.
How to change subscription limits if Web admin license is installed in Plesk?
Connect to Plesk server using SSH or RDP and use "plesk bin subscription_settings" command:
# plesk bin subscription_settings -h
For example, to set disk usage to Unlimited on Linux:
# plesk bin subscription_settings -u example.com -disk_space -1
Or to set MS SQL databases limit to 50 on Windows:
C:> plesk bin subscription_settings --update example.com -max_mssql_db 50
To check the results find a corresponding limit in the output of the command (Linux and Windows):
# plesk bin subscription_settings --info example.com
To set Unlimited for all subscriptions on Linux
To set different limits for a subscription/webspace, refer to CLI guide for Linux and Windows that contain detailed explanation on how to use the commands, what limits can be set and how to set them up.