Preparing to Desolder
Now you will solder the component you want to remove. Yes, you read it right. You may be asking yourself why you should solder the component if you want to desolder it. Actually, this is a very powerful trick to allow old solder to be removed. What happens is that old solder (many years old) is very hard to be melted by the soldering iron and sucked by the solder sucker. So what you will do is to mix new solder with old solder. This mix is easier to melt and to be sucked.
There is another trick to be used during this process. With the soldering iron tip you should push the terminal back and forth in order to make it lose from the border of the hole. Many times the terminal is stuck at the border of the border, making it hard to be removed. You should repeat this process at least two times in each direction. After swinging the terminal with the soldering iron tip, you should leave the terminal more or less in the middle of the hole.
In the photos below we show these two tricks separately, but you should do the two things at the same time, also because swinging the component terminal helps to mix the old solder with the new one.