Answer: 

During auto-upgrade, DS-Client downloads from DS-System the corresponding upgrade package and change its name to dsclni.exe (Windows DS-Client) or dsclni.bin (Linux DS-Client). If the auto-upgrade fails it is recommended to try a manual upgrade following the procedure described below:
1. Logon in Windows the DS-Client machine with the DS-Client service account (check first in Start > Administrative Tools > Services what is the service account for the service called DS-Client)
If the DS-Client service account is Local System, you will need to logon in Windows with a user that is member of local Administrators group one the one hand, and that has granted the sysadmin role for the SQL Server instance holding the DS-Client databases on the other hand;

2. Navigate to DS-Client installation folder (default C:\Program Files\CloudBackup\DS-Client) and double-click on the file called dsclni.exe, the DS-Client setup menu will open, just go through those panes to complete the upgrade (you will pretty much need to just click Next on each pane since this is an upgrade).

To manually upgrade a linux DS-Client that failed the auto-upgrade:
1. Logon as root on the DS-Client computer and open a terminal.
2. Navigate to the DS-Client installation folder, upgrade sub-folder using the command:
cd /opt/CloudBackup/DS-Client/upgrade
if DS-Client was installed under a different path, update the command accordingly.
3. Launch the DS-Client setup using the command:
./dsclni.bin
The DS-Client setup menu opens, go through all panes to complete the upgrade, you will mainly just need to click the Next button.