ISSUE SUMMARY:
Hi there,
Currently I am running version 4.0.7 on my site but when I try to access the backend of Jomsocial I get the errror:
Fatal error: require_once(): Failed opening required '/home/graphiqs/public_html/www.driverz.club/components/com_community/models/community.php' (include_path='.:/usr/local/php55/pear') in /home/graphiqs/public_html/www.driverz.club/components/com_community/libraries/core.php on line 656

On a local test environment i have installed version 4.2.6 pro because the iJoomla installer gives a blanc screen after clicking the update button. After the succesful installation I still get the same error. Also when I navigate to the iJoomla installer it gives the following warning:
In order to upgrade to JomSocial 3, you must first upgrade to 2.8.4.2 first and then upgrade again to JomSocial 3
But as said I am upgrading from 4.0.7 to 4.2.6.

On my production site I have not tried this to have you guys see exactly what is happening when you try it. I have a backup of the site so you can test it yourself.

STEPS TO REPLICATE:
1 Login to the site and navigate to the Jomsocial component
2 After this try to update from the iJoomla installer
3 After this install 4.2.6 from the Joomla installer

RESULT errors
EXPECTED RESULT working backend
BROWSER Chrome

HI, Ewoud.

Thank you for contacting us.
Error indicate that file is missing. So please, try those steps:

0. Make a safe copy of your whole system (files and database)
1. Browse to Backend -> Extensions -> Extension Manager -> Manage
2. Search all extensions using filter "com"
3. Uninstall all JomSocial related extensions
4. Search all extensions using filter "jom"
5. Uninstall all JomSocial related extensions
6. Download latest JomSocial package from here: www.jomsocial.com/component/digistore/licenses
7. Unzip it
8. Install com_community package via Joomla! installer
9. Follow installation steps

Thanks, on my testing evironment it is working. I will need some time to do this on my production environment but for now I am helped with your answer.