Hi Srini
it is possible to change from DB to DBFS --
Following would be basic steps :
a) Check space in File system to ensure that data can be migrated.
b) Change the configuration of the CM repository manager. In the Root Directory parameter, specify the path to the file system where the DB needs to be stored. Change the entry in the Persistence Mode parameter from DB to DBFS.
c) Application SAP needs to be restarted.
d) Run the CM Store: Content Crawler report.
Please see following thread also - Setting up KM reporsitories in DBFS mode | SCN
Following link is helpful - CM Repository Manager - Knowledge Management - SAP Library
Thanks
Rishi