Removing solder effectively
The problem you are facing is that 30W can't produce enough heat to melt solder that is in contact with a lot of metal and consequently works as a heatsink.

Best option is to buy a temperature controlled soldering iron that has a higher wattage, the advantage of that is it can reheat the tip very fast when it detects that the temperature is dropping by providing 50w or 70W or even more (depends on the model).

The cheap alternative is the heat gun which is powerful enough to melt the solder but has no temperature control so it's up to you to control the applied heat.

My suggestion if you intend to use the heat gun is to put some solder paste (avoid inhaling the fumes) on the solder you want to remove which will help it melt when heated, place a desolder braid over the solder  and heat it with the gun from the opposite side (The order is I mean is in layers from bottom to top : solder / paste / braid / soldering iron , in a sandwich fashion). This way you will be able to remove the solder little by little without overheating too much the surroundings by sucking the solder in the braid as soon as it melts .

Finally there is always the despair solution which is to cut the wires as close to the end as you can and resolder them to the new plug (assuming they are long enough)