You'd be better served just buying a 510 connector at
madvapes for a buck twenty nine or at kens box
mods for a buck seventy nine.
That said: A pair of pliers, a vice, and a nice soft piece of cloth will be necessary. Put the battery in the vice, put the cloth around the 510 connector, and grip the cloth with the pliers. Take it easy and don't smash the pliers down too hard - twist and wiggle it back and forth until the connector comes out. Don't yank it because there's wire soldered to it. Once you've pried it loose, heat of the solder for the wires with your soldering iron and remove them.