1. Verify the current version and the target release's requirements and customisation changes.
2. Back up the database and all application files and test the update on an isolated copy.
3. Download the authorised full release or applicable patch set from your licence provider.
4. Extract it locally and map its administrator and cron directories to any custom paths in your installation.
5. Protect the existing configuration.php and preserve your separately maintained customisations.

For a full release, upload the package into the existing WHMCS installation and complete the browser update at the installation's install/install.php address. Read the backup confirmation and monitor the result. If the application reports that WHMCS is not installed, inspect the configuration file before starting a fresh installation.

A patch set is for its specified starting version. Follow its release instructions and do not treat it as a complete distribution that can update any old installation. Never mix a patch for one branch with files from another branch.

Remove the installation directory after the update succeeds. Restore any intentional permissions required for cron or email piping, and check that renamed administrator and moved cron locations received the new files.

Merge required template changes into your custom theme. Uploading an older customised file over a new release can reintroduce the very compatibility problem the update resolved.

Check the version, system health, sign-in, checkout, invoices, support and scheduled automation. Keep the original backup until the important integrations have passed.

If a database update failed, preserve the exact error and current files. Restore the matching database and file set when rollback is necessary; replacing only one side can leave incompatible application and schema versions. Use the documentation for your target version when confirmation labels or update behaviour differ.

• Use the WHMCS automatic updater safely
• Plan an upgrade from an unsupported WHMCS version
• Back up and restore the WHMCS database and application files
• Maintain a custom WHMCS theme across upgrades

• WHMCS: update in the browser
• WHMCS: updating WHMCS