Drobo 5N change 3DD 6T 10T and no result


I my Drobo 5N have 5 6T hard drive. So because I have only lefts160Go left I decide to replace 3DD by 3DD 10T.
So the configuration now his
Slot 1 10T
Slot 2 10T
Slot 3 10T
Slot 4 6T
Slot 5 6T

Now the result I stil have the same amount of space. What I miss, why I do not have any more data space. I was thinking those add il will att les 2T more DD available

Please note

All my Hard drive are WD RED

Than you