PaulS is referering to the Reset Enable trace that is between 2 solder pads.
If you cut the trace, then DTR is no longer connected, requiring manual intervention with the Reset Button to download sketches, not that big a deal.
(Press & hold reset, when the IDE indicates "Sketch xxxxx byte of 32xxx byte" (something like that) then release the button.)
You can later go back and solder the 2 pads together if you want to use DTR again.
The trace is in the little box next to the big crystal, labeled "RESET EN", or maybe "RE ET EN" if you look at Uno R3 picture in the hardware section.