A common pattern I perform in MacPorts is embodied in the following function.
function update_macports {
sudo port selfupdate
sudo port sync
sudo port outdated
}It updates MacPorts, syncs the ports database, and then shows me what is outdated. For most ports I tend to uninstall the old version and then install the newer version. Sometimes this gets you in a never ending dependency removal loop.
Use sudo port uninstall --follow-dependents your-portname-here. This will uninstall this port and any dependent ports not in use by other ports on the system. Useful for cleanup after experimentation.