I think that the qBittorrent allows quite simple bulk relocation of the multiple torrents.
But i not wanted to mess with the qBittorrent configuration anyhow, so i just linked onld folder to new folder using "mklink" MS WIndows tool.

0. quit qBittorrent and make sure process is not running
1. In WIndows explorer, open new location of the files and copy the full address into clipboard.
2. click WIndows icon (menu)
3. type on keyboard: "cmd"
4. right click cmd.exe and select to run it as Administrator
5. Now add following example command and edit it to fit your old and new path:

mklink /D "C:\MyOldDirectory" "X:\New Directory"

(this command creates an directory symbolic link which should redirect apps that are using MyOldDirectory to the New Directory.)

6. start qBittorrent, qbt 4.1.4 apparently automatically start rechecking torrents that had missing files status.