Update theme and PHP

Seeking assistance with Unicon theme.
-Purchased Unicon v2.4.1 3/2018
-Downloaded first update available v2_7_3. I see in the notes there was a major update a while back, but I did not receive notification of it.

Issues:
1-when I install updated theme using ftp, the site does not function. Even WP Admin backend does not work.
2-need to update PHP from current v5.6 to v7.x, but unable because that also causes site not to function.
3-I hope the new Unicon v2_7 includes updated WPBakery, because current v5.4.4 which came with Unicon theme is out of date.
URL: https://www.growthgps.com

I welcome your hands-on assistance; I like Unicon very much. I am not a technical website developer and want to keep this site updated and protected. This website is critical to my business.
Thank you, Keith

Ticket