How did you prep your hard drive and install PFS initially? The procedure is virtually the same.
The summary version is:
1. Extract pfs3aio.lha
2. Copy pfs3aio to L:
3. Open HDToolbox
4. In the partitioning screen, choose Add/Update Filesystem
5. Select the existing PFS, choose Update
6. Select L:pfs3aio
7. Save changes and reboot.
The details will vary slightly depending on your OS version. There may be other things you need to adjust, e.g., DOSType, but hopefully not. Either way, it sounds like you're not very familiar with this kind of procedure, in which case you should make absolutely sure that you have a full drive backup in case something goes wrong.