Stop QuickBuild server of previous version, you do not need to stop agents since they will be auto-upgraded after server is upgraded.
On Windows, run <old installation directory>/bin/service-uninstall.bat to uninstall QuickBuild NT service of previous version if necessary.
Extract installation package of new version to a new directory.
Open a command line window, and switch to the bin sub directory under the new version's installation directory. Run the migrate command to migrate from previous QuickBuild version. On Windows platform, the command is migrate.bat <install directory of previous QuickBuild version>, and on unix platforms, it will be migrate.sh <install directory of previous QuickBuild version>.
Start QuickBuild server in new installation directory and agents will be auto-updated. It will take a while for them to appear in the build grid.
Verify server and agent installation by running some builds.