Resizing MAY require you have enough free space to do the task. Also,
on the utility I use, the actual resizing takes place during reboot, which you must do just after setting your resize options.
The steps are; resize first creating a free/unused partition, reboot, then format the new partition.
I use
Partition Magic on my home PC, a very good utility for this task IMHO.
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Tecknomage
Computer System Specialist
IT Technician