Heat, de-solder and suck the old solder off.
I use a sharp round pick after I pull the solder off. I insert it and make sure the hole is de-burred. Clean the pins or wires with a little isopropyl, insert them through the cleaned up holes and little dab of flux and solder. Clean afterwards with isopropyl alcohol. Check your work. If there is any issues, repeat the process.
It will take longer to heat up the soldering iron than to do the work. :-)