you dont need the synaptic manager to install anything: all you need is a commandline:
will update the package information and get the new info from the servers in you /etc/apt/sources.list
sudo apt-get update
Will install any upgrade to the software that - to put it simple - will not remove anything to resolve dependencies.
sudo apt-get upgrade
This does an upgrade like the forementioned, but will also resolve dependencies and install most of what was "held back" in the one above.
sudo apt-get dist-upgrade
will search for anything available containgin "chatIamLookingFor"
apt-cache search whatIamLookingFor
will install the package "whatIwantToInstall"
sudo apt-get install whatIwantToInstall
as an example would install the package called "samba" and everything this package needs (aka dependencies)
sudo apt-get install samba
As for the resolution issue:
If you could provide us with the info on what graphics card you are using, we might be more helpfull at the basic problem of your screens resolution.
As a hint: once again on terminal: or should give you some line containing info on your graphics card/adapter that could be helpfull here.