I have a speciality computer that has an 8 GB flash memory card for the system disk, /dev/sda, and a 256 GB removable SSD, /media/sdb, which will be used for data. It has no optical drive and I have no USB optical drive. We underestimated the amount of space needed for the system disk so I get warnings when I log on and have had as little as 30 MB free space. For a short term solution I backed up the data on data disk and used dd to clone the system disk sda to sdb and then rebooted.
I have gparted installed so I unmounted sdb and attempted to enlarge sdb1 to 15 GB (which should fit into a new 16 GB flash drive) for the system and swap space. I intended to put the unused space into a new partition. gparted won't let me change the size of sdb1.
I thought that the proper course of action to be able to boot into sdb would be to enlarge the partition, change the UUID somehow, edit /etc/fstab and perhaps some other files and I'd be good to go. It appears that I'm wrong. There's a nice tutorial on gparted on this forum but it sheds no light on my problem.