I'm not sure if HP includes backup software similar to Norton Ghost. If so, use that. Otherwise, you will need to acquire backup software which will make an exact copy of your drive.
Once you've done that, you need to do the following:
- Use the software to do a backup.
- Uninstall your current drive and install the new one.
- Restore the data from the backup onto your new drive.
After that, it should be done.
Note that things may be slightly different depending on your circumstances.
EDIT: Maybe you can even keep the other hard drive installed so you can have 380GB total space.