Once an addon has been installed, and subsequently the developer of the addon releases a new version, it will be possible to upgrade the addon as follows.
Although it is an addon developer's responsibility to make sure that addon upgrades execute smoothly, and preserve data from the previous version, one can never be sure. As such, it is important to make a copy of your TIki site and conduct the upgrade on the test site first.
Similar to when Installing Addons, you have to obtain a copy of the addon package and place it in the addons folder, REPLACING the version that exists there. It is recommended to move the existing folder e.g. addons/vendorname_packagename away to a safe location and then extracting the new version there.
If you are getting your packages via composer (advanced), it will be enough to change the version to be picked up in your composer.json file and it will automatically update it when composer is run.
To complete the upgrade, execute in the folder where you installed Tiki, replacing vendorname_packagename with the actual name of package you are upgrading.
php console.php addon:upgrade vendorname_packagename
Then test your newly upgraded addon. if all works well, you are then ready to upgrade your live production site using the same process.
Depending on the specific addon, it may not be possible to upgrade from every version to another version. The developer of the addon sets this information in a file "upgrade.json" that is shipped with the addon. The developer should also have documented this information on the addon's website. If you are a few versions behind, with some addons you might have to do multiple separate upgrades instead of just one, to get it to the latest version.
When running the upgrade command above if you do not have installed one of the versions, it will tell you so.
Depending on the specific addon, it could depend on a specific version (or minimum version) of another addon being already installed. The developer of the addon sets this information in a file "tikiaddon.json" that is shipped with the addon. The developer should also have documented this information on the addon's website.
When running the upgrade command above if you get error messages saying such and such profile and so on are not yet installed, you are probably missing a dependency.