Use the zoom tool to make a new view to display only the lips and the tip of the lipstick. Close any zoom views that are no longer required.

Use the eyedropper to select a new lip color. Pick red (RGB 255,0,0) using the color palette menu. Select the tint button in the effects tab. Note: this will de-select the lighten button. Press down and hold the cursor in the color box to set the tint color to the current color.

Select layer 1 by clicking on the layer with that name in the layer list palette. Make sure that color mode is active.

Select the freehand tool, trace around the perimeter of the lips and the top of the lipstick. It may take you several attempts to get the best result. The lips will have now been tinted using the tint color. The teeth will have also been tinted to some degree so to remove this effect we need to apply a further mask.