Router Slate AX.
So I filled the Flash storage with a torrent file and now I don't know how to get rid of it. I did uninstall the Transmission torrent from GUI and from Luci, but Flash storage ( NAND Flash 128MB ) on the router is full. 
edited for typos.
I think we would like to know what processes/plugins occupy the RAM and full?
Not RAM, sorry it was a typo. Flash storage ( NAND Flash 128MB ), where you know, entire OpenWrt is installed. Thats where I downloaded a torrent by accident while trying to set up Transmission torrenting program.
I did a full reset of the router and that might have solved the problem??
Can you please verify the image I have attached, that the "Flash" storage has been properly erased?
Cheers.
Resetting the router will clear the flash as well, so now you are good.
I did perform a reset. Is the available space shows accurate information?
Cheers.
Not related to the problem, but Jack Swigert said: "Okay, Houston, we've had a problem here."
It shows how the memory is used so... yes, it is accurate at this point.
Looks like I didn't reset the router correctly. In order to delete all the files and settings, the router has to be reset from Luci and not from GUI.
And here is what it should look like;
I am not sure if this is correct, tbh.
The reset procedure should be the same. Easiest way for a full reset would be to install the firmware without keeping settings.
Im glad you mentioned, because I did that as well. 
Cheers.