You can't do apt-get update
from the command line of the update manager.
To run the command, use
update-manager
man update-manaer
gives:
--data-dir=DATA_DIR
Directory that contains the data files
-c, --check-dist-upgrades
Check if a new distribution release is available
-d, --devel-release
Check if upgrading to the latest devel release is possible
-p, --proposed
Upgrade using the latest proposed version of the release
upgrader
--no-focus-on-map
Do not focus on map when starting
--dist-upgrade
Try to run a dist-upgrade
so you can move over by running
update-manager --dist-upgrade