If you try to upgrade Deskpro and get an error with something like this:

...
[EXCEPTION] GuzzleHttp\Exception\ConnectException:0 cURL error 28: Connection timed out after 5001 milliseconds (see http://curl.haxx.se/libcurl/c/libcurl-errors.html) (/app/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php:186)
...

It means the upgrader could not connec to the Deskpro download server to download the latest version. This is often caused by a firewall or security software (including SELinux). You'll need to get your sysadmin to lift these restrictions if you wish to use the automated installed.

The alternative is to manually install the update from the command-line as outlined in the manual here:

https://support.deskpro.com/en/guides/sysadmin-guide/upgrading-2/manual-updates-2

This uses the same routines as the normal upgrade system, but if you run it manually as a privileged user, it may bypass security restrictions.

If that continues to fail with the same message, the only remaining option is to download the files manually and install them yourself as described here:

https://support.deskpro.com/en/guides/sysadmin-guide/upgrading-2/update-from-source-2