This indicates that repositories have changed or added information concerning their software. The changes/additions are to software version information 'tags' so can reasonably be expected to change during the support of software.
The update/upgrade process requires indication from the user that these new labels are OK which is done by running from a terminal
sudo apt-get --allow-releaseinfo-change update
This allows the update process to continue. Once updated
sudo apt-get upgrade
should be run to complete the job