In order to upgrade another catalog, please open LR 6 and then click on File>Open Catalog.
And then please select the location of the catalog that you want to upgrade, it will give you the prompt to upgrade the catalog.
Unfortunately that does not work. As described it does nothing at all. No dialog, no opening, just nothing.
Could you please check and let me know what is the size of the Catalog that you are trying to upgrade.
The catalog is 11 Mb.
It's a catalog containing only of video files (quicktimes) I am using LR to organize my videos.