You can manually update via terminal by running:

sudo apt-get update

sudo apt-get upgrade

Additionally you can run:

sudo apt-get dist-upgrade

From the apt-get manpage:

dist-upgrade in addition to performing the function of upgrade, also
intelligently handles changing dependencies with new versions of
packages; apt-get has a "smart" conflict resolution system, and it
will attempt to upgrade the most important packages at the expense of
less important ones if necessary. The dist-upgrade command may
therefore remove some packages.