If arch or tube punches are of soft enough metal, they can be sharpened
with a file.  If they are harder a whetstone or grinder is necessary.

I use a die grinder and magnifying safety glasses.  This is easier, for
a few punches, than setting up a grinding fixture.  Make sure to grind
only the beveled edge if you want to keep the punch the same size.
Also try to keep the bevel angle the same or you will change the
cutting ability and or strength of the punch.

Spencer Chase