To Delete Design History

Select File > Settings > Configuration > Configuration Variables .
The Configuration Variables dialog opens.
Select the MS_DESIGN_HISTORY configuration variable.
Click Edit.
The Edit Configuration Variable dialog opens.
In the New Value field, type delete=1.
Click OK, then click OK again to close the Configuration Variables dialog.
Verify that you want to save changes to the user configuration file.
Exit and restart MicroStation.
Do one of the following:

In the status bar, click the Design History icon and select Delete from the pop-up menu.

or
Select Drawing > Utilities > Design History > Delete .
Click OK to verify that you want to delete the design history.
The design history for the file is deleted.