Updating my theme and site check error's

This is my first site in the making so i am new to all this. I bought your them back in May 2017. I have been working on it since. First i have been informed there is an update to the theme so i wish to do the update soon. I have downloaded the update zip and have configured filezila. But i am very worried of loosing all the work i have done by updating in the wrong way. I have made some backups of my site, but would like to know the correct way to do this without having to use them. One thing i did not know to do was to make a child site before i started work. Is that now to late to do or can i still make a child site now. I did a site check from WP and it gave me the following errors WARNING WP_DEBUG is not enabled! Please test your theme with debug enabled before you upload! It then gave me the following errors:-
One or more errors were found for TravelWP.

Warning: More than one text-domain is being used in this theme. This means the theme will not be compatible with WordPress.org language packs.
The domains found are travelwp, woocommerce
REQUIRED: Zip file found. Plugins are not allowed in themes. The zip file found was js_composer.zip revslider.zip physc-vc-addon.zip travel-booking.zip home.zip video_slider.zip.
RECOMMENDED: Possible variable $login found in translation function in inc/widgets.php. Translation function calls must NOT contain PHP variables.

Line 793: echo json_encode(array(‘loggedin’=>true, ‘message’=>__($login.’ successful, redirecting…’,’travelwp’)));

INFO: Non-printable characters were found in the inc/physc-selector.php file. You may want to check this file for errors.

Line 13: ‘H��me 3’ => array(

Line 18: ‘H��me 4’ => array(

Would it be better if you logged in and sorted these small things out for me, i do not want to loose all the work i have done so far.
Regards
Mark