Increase space TSM Database

[Hafizan]

hi,

When i issued command "q db f=d"

    Available Space (MB): 20,000
        Assigned Capacity (MB): 19,828
        Maximum Extension (MB): 172
        Maximum Reduction (MB): 248
             Page Size (bytes): 4,096
            Total Usable Pages: 5,075,968
                    Used Pages: 5,012,336
                      Pct Util: 98.7
                 Max. Pct Util: 98.7
              Physical Volumes: 20
             Buffer Pool Pages: 8,192
         Total Buffer Requests: 8,053,712
                Cache Hit Pct.: 97.26
               Cache Wait Pct.: 0.00
           Backup in Progress?: No
    Type of Backup In Progress:
  Incrementals Since Last Full: 0
Changed Since Last Backup (MB): 390.96
            Percentage Changed: 2.00

Pls advise me how to increase space  TSM database.