When a new version of a package has been released, it is easy to install it on your system. Select the packages from the window of available packages in the same way you select packages for installation. Both the Upgrade button and the context sensitive menus will begin the upgrade.
During the upgrade, you'll see a progress indicator like the one for installing packages. When it's finished, the installed packages will appear in the the main glint windows and any old versions of the packages will be removed.
It is much better to use the upgrade option than to uninstall the old versions of a package and then install the new one. Using upgrade ensures that any changes you made to package configuration files get preserved properly, while doing it manually could cause those changes to be lost.
If you run out of disk space during an installation, the install will fail. However, the package which was being installed when the error occurred may leave some files around. To clean this up, reinstall the package after you've made more disk space available.