Hi Kedar
Sorry for the delay in replying
In your situation if you want to make full use of device use disk resize to make to 10 GB.
One logical device can have chunks allocated to many databases.
That is not an issue. Best practice is not to have data and log (for any databases) on the same logical device. So once you create a logical device allocate only 'data' or only 'log' on it.
If you want to free up the device and start over again
- use mirroring or
- full backup and restore mechanism to move the current database to new device.
Then drop old 4 GB device and recreate new with required 10 GB capacity.
HTH
Avinash