I have partially uninstalled (removed files manually) of the CFT on windows platform.
Now, when I want to install it again, it failed because the product is found as already installed.
How can I remove completely the actual installation to restart from scratch?

Verify whether are there any files related to CFT, you can search those files using CFT*. In general you can find those files in WINDOWS (cft.ini) folder and SYSTEM32 (CFT dll's) folder. After deleting all remaining files you should be able to start the CFT installer again.
It is also recommended that you always uninstall the product through the installer program to avoid such a situation.