Do be sure to back up all of your photographs in some manner; online/cloud storage, NAS, portable storage, etc., before tweaking partitions, and so forth.
At least two full sets. Use backup software or simple Copy commands (not Move).
Ensure that the backup locations are physically isolated from the current host system.
Ensure that those photo backups are recoverable and proven readable.
If the partitioning somehow goes astray then you will still have copies of the photographs.
Plan the re-partitioning process all out, step by step, before actually starting to do so. Know what to expect with each step and the desired end results.
May catch some error of omission or commission that you can correct (or do over) before things become irreversible.