Note: These steps are if you are upgrading WHMCS 7.10 to WHMCS 8
We are excepting that you already have an updated theme according to Whmcs 7.10.X
Step 1: Download the patch folder "WhmcsV8.X.X--HostxV2.1.1-TemplatePatch.zip"
Step 2: Extract the patch files
Step 3: Take a Complete Backup of your WHMCS Instance (Highly Recommended)
Step 4: Override the template folder at whmcsdir/templates/hostx
Step 5: Override the orderform folder at whmcsdir/templates/orderform/hostx
Step 6: Override the addon folder whmcsdir/modules/addons/hostx
That's it you have upgraded the version.