It's best to backup your Gateway before upgrading Ignition. See Gateway Backup and Restore.
From Gateway, go to Config > Backup / Restore.
Click on Download Backup to back up the entire project from the existing installation.
.gwbk backup file is created in the Downloads folder.
Shut down Ignition by typing the following from the command-line:
Move the existing installation folder somewhere else.
Unzip the new installation and place it in the location of the old installation.
Start the new installation.
Go to Config > Backup / Restore and click Restore to perform the restoration.