Purging of some of the versions of a model with the erwin Workgroup Edition (Model Manager) r8/r9 Version Manager will reduce the query processing time when opening a model from the Mart. However, that will not reduce the size of the mart database, and that will not give you more free space in the Mart database.
To shrink the mart database or to reduce the size of the mart database, you must release the data of the purged model versions from the mart (think Windows recycle bin). That must be done with the Reorganize or Shrink function of your database management tool.
The following is an example using Microsoft SQL Server 2008 r2:
Start Microsoft SQL Server Management Studio
Expand the databases in the Object Explorer
Right mouse click on the Model Manager database name
Click on Tasks | Shrink | Files
Select the option "Reorganize pages before releasing unused space"
Set the Shrink Value to the same value as displayed in the "Currently allocated Space" field if you want to release unused space only.