When you get your corset, you will see its already laced up at the back. If you have purchased a modesty panel you will see it is held in place by two loops of which the laces run through.
There is no need to take the laces out, just undo the knot/bow at the middle waist line and slacken the laces, opening the back as far as it will go. Once the corset is slack put the corset around you and fasten the front busk. Tighten the corset laces from top to waist and from the bottom to the waist. You can repeat this process until you get the correct tightness then knot the loops at the waist. You may be able to tighten the corset some more after wearing it for a little while but don't over tighten your new corset. It takes a little while for the corset to take your shape.
The knot at the bottom should not be undone unless you want to remove the modesty panel in which case the laces will have to be removed completely. The aglets are easily removed using some pliers.