It is recommend to always backup your system before making any upgrades or changes. A database backup is highly advisable.
Firstly, make sure the OpenCart version you want to upgrade to is supported. This should be noted in your theme’s official page and documentation. The theme package itself does not upgrade your OpenCart installation to higher version.
The .zip archive from Themeforest contains only theme related files. If you want to upgrade to higher OpenCart version, you must download and apply the new OpenCart update from the official OpenCart site.
Upgrade OpenCart from 2.0.x/2.1.x to 126.96.36.199 and above
Since OpenCart 2.2, themes have been detached from modules and have own section in the admin panel – Extensions › Themes. This means, if you upgrade your OpenCart installation from 2.0/2.1 to 2.2+, BurnEngine will appear as new theme under Extensions › Themes. If you click install there, you will loose all your previous theme settings, as it will be installed anew.
To avoid this, use the BurnEngine export tool to backup your theme settings first. After the OpenCart upgrade and theme installation, you can import these settings back.
Upgrade your theme
Download the latest version of your theme from your themeforest account. Make sure it supports the OpenCart version you are currently using.
1 Unzip the downloaded package and re-upload the files to the root OpenCart directory, overwriting the existing ones.
2 Enter the BurnEngine control panel – you will see a message to confirm the upgrade to higher version:
3 Re-save your theme settings and the settings for all built-in extensions.
Note that error notices may appear on your site in the period between uploading your new files and clicking on ‘Upgrade BurnEngine’ button. That’s why it is recommended to enter ‘maintenance mode’ before uploading and applying the upgrade.
Because BurnEngine comes bundled with your theme package, there is no separate upgrade. A theme upgrade is also a BurnEngine upgrade.
If you want to upgrade OpenCart and your theme at once, you must first upgrade OpenCart and then the theme (assuming the theme supports the OpenCart version your are upgrading to). After upgrading OpenCart, make sure everything works fine with the default theme enabled. This will help you to distinguish the eventual OpenCart issues from theme issues.
If you have manually modified some theme files and you don’t want to overwrite them when you upload the upgrade, you can take a look at the files changelog. You could copy only these files which have been changed since your last update. If you have hard times comparing and updating the changed files, check how you can easily compare two files.