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Each HostBill is shipped with Auto-Upgrade, an the enabled by default plugin that is built to make upgrades & patches easier and faster. Plugin is located under Extras → Auto->Auto-Upgrade. If it's not enabled you can turn it on under Extras ->Plugin → Plugins in your HostBill Adminarea.
Before using Auto-Upgrade for the first time
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Before using upgrade or patch for a first time, make sure you've created backup of both of your HostBill files and database. Use controlpanel control panel backup option or manual db dump (mysqldump, phpmyadmin or simmilarsimmiliar). This plugin do not perform backup on its own.
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When new version is available you will see notification on the top of the admin home page:
After going to Extras → Auto->Auto-Upgrade you will be able to apply upgrade with one mouse click.
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A: No, as long as you keep your custom templates in separate folder under /templates, if you've modified some files its it's safe to make custom folder under /templates and keep your entire look there.
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