How do you refill a BIC 4 colour pen?

To refill a BIC 4 Colour Pen, first, unscrew the end of the pen to access the ink cartridges. Carefully remove the empty cartridges by pulling them out; note the color order for reassembly. Insert new cartridges into their corresponding slots, ensuring they are securely in place, and then screw the end back on. Test the pen by clicking each color to ensure proper ink flow.