Important
It is highly recommended to install the theme on a test server before you install it on your live store
Backup
Backup store files and the store database.
- Disable the following options: Merge CSS Files, Enable Javascript Bundling, Merge JavaScript Files and Minify JavaScript Files under Stores > Configuration > Developer.
- disable Magento cache – Cache Management
- Enable Magento maintenance mode. To enable the maintenance mode you can create a simple empty file named .maintenance.flag in your Magento’s var directory. Magento will be offline after that. You will need to disable the maintenance mode after installation by removing this file.Refer to Magento documentation for more details:
http://devdocs.magento.com/guides/v2.0/installgde/install/cli/install-cli-subcommands-maint.html#instgde-cli-maint - Log out from magento admin panel ( if you logged in ).