You want to remove the whole stem, if you just cut the leaf off the stem will only rot.
I find it easier to remove them by hand if there's enough space in the tank - if you run your fingers down the stem (and probably under the substrate a bit) you'll feel where it joins the rhizome, and if you bend it away from that it should snap off - if you just cut it off at or above the substrate level the underneath part will still rot - not normally a big problem, but especially if it's a new tank you want to avoid that as much as possible.
New leaves can only grow from the rhizome, the old stem will just perish.
Mark