RAM File System isn't a new version of RAM Disk. It is a separate product with a completely different architecture.
RAM Disk creates a virtual disk that Windows then formats with NTFS or exFAT, whereas RAM FS is a file system in its own right, with no disk emulation and no NTFS/exFAT layer underneath. That's what makes it noticeably faster.
So there is no direct upgrade. But there is also no need to uninstall anything first if you have enough RAM. The two products can happily run side by side, which makes the switch very easy:
- Install RAM FS. Leave your RAM Disk exactly as it is for now.
- Create a RAM FS volume on a free drive letter. Keep an eye on RAM usage while both are mounted - they each use their own.
- If you have anything important on your RAM Disk, copy those files across.
- Update everything that points at the old drive to use the new drive letter (for example, 'TEMP'/'TMP' variables, browser caches, etc).
- Reboot and check that everything works as expected.
- Once you're happy, uninstall RAM Disk.
If you prefer your new RAM FS volume to use the old drive letter that your RAM Disk was using, remove the RAM Disk volume first so the letter is free, then create the RAM FS volume with that letter. The letter is chosen when the volume is created, so it's worth deciding before you copy your data over.
One note: the existing RAM Disk image files can't be loaded by RAM FS, as they are in NTFS rather than in RAM FS own format, so you should copy the files across as above rather than moving the image.