How to extend HD logging space?

Dear all,

I have a F1500D Fortigate FW and only use single vdom "root" but by default the logging space for each vdom only 33Gb. How can i extend logging space. Please give me your advice. Thanks a lot!.

Total HD usage: 37037MB/112673MB Total HD logging space: 33802MB Total HD logging space for each vdom: 33802MB HD logging space usage for vdom "root": 31219MB/33802MB