I have installed 7.5 and the progress was 7.0 -> 7.2 -> 7.5
However, when I click "Insert Link", "Media Link.. " and some specific link in content editor, Sitecore says the dialog path can not be found.
So, I knew that Sheer UI (old UI) replaced with SPEAK UI from 7.2. Many articles (https://briancaos.wordpress.com/2014/07/02/disable-sitecore-speak-dialogs/) says that I can comment out "overrideDialogs" node in "Sitecore.Speak.config" file to keep using old UI. But, the nodes are located at "Sitecore.Speak.Applications.config" file, not "Sitecore.Speak.config" file.
I tried to comment out the node in "Sitecore.Speak.Application.config" file, but it doesn't make the dialog UI pop up and it shows me the same error.
How can I change this back to use old dialog UI in 7.5? Or, how can I enable SPEAK dialog UI in 7.5??
How about taking a brand new 7.5 install and copying the "sitecore" directory to your existing, upgraded instance?