If I have a darker shade of paint, can I have it changed & lightened to 3 shades lighter on the color sample chart?
Sure. You can even do it yourself, if you want to.
For blues, grays, greens and neutrals: add white.
For other colors (reds, browns etc), you can do that too, but if the color gets to pale for your taste, add some brightness to it with a little extra yellow-orange (reds) or magenta (browns).
Good luck, Evelien