ECM prerequisite check for update from 1910 to 2006 fails because of disk space

Dear community.

I want to update my ecm from 1910 to 2006. I have a main Server and a site server in an other office. Today i made the precheck for the update to 2006 and the check failed with the message "Check that the site server computer has sufficent available disk space to install the site server".

I am a bit confused, there is already an ECM site server running on that computer but the precheck talks about "install" and not "update". Is this correct ?

How much disk space is needed for that update ? On C:\ i have at least 30 GB free and on disk D:\ where all the Update data and the OS images are, there is also at least 30 GB free. Is this not enought for that update ?

Thank you very much for feedback and your help