Giving names to partitions so that when they are automatically mounted you get a meaningful name instead of an UUID or as Nautilus does 250 GB File System is a handy way to help keep things organized.
Unmount the partitions before trying to change their labels
The tool for ext2, ext3, and ext4 file systems is e2label. The first line shows the current label for the specified partition and the second command will change it.
e2label /dev/sdh1 e2label /dev/shd1 Partition_Name
The tool for reiserfs partitions is the reiserfstune program which is part of the reiserfsprogs collection of tools. As with e2label the first command below will show the current label if any and the second changes the label.
reiserfstune /dev/sdh1 | grep LABEL reiserfstune /dev/sdh1 -l Partition_Name
For more information see the man pages for commands.