There is a known issue in TLXOS RPi 4.9.2 that will prevent upgrade to any
later version (such as 4.9.3) on Pi models with 1 GB of RAM.

Please install the hotfix named "fix 1GB RAM upgrade error" prior to upgrade
to resolve this issue.

If you have tried to upgrade without this and are now stuck in a never-ending
failing upgrade loop, using TMS' "Device->Commands->Exit Upgrade Mode" option
twice in a row (while the client is still responding to TMS) will get you out
of the loop.  The first time it will abort the upgrade attempt but fail to
exit Maintenance Mode, the second time it will actually exit Maintenance Mode.