First thing to do is undo your quick release and remove your front wheel. Try not to touch the disc brake pads, which will contaminate the disc pads and cause a squeaky sound when riding.
Next thing is to remove the disc brake pads. Remove the bolt at the bottom of the caliper. Put the bolt to the side. To remove the pads, push from behind.
Make sure the new pads are correct by measuring them up to the old pads. Insert the pads back in, making sure the two holes are facing towards the back. Make sure not to press the brake while doing this job, so you don’t seize the pads on the pistons. Pop the pin back in and screw it so it is tight.
Last thing to do is fit the front wheel back in. Make sure it is straight between the forks. Close the quick release and you’re ready to adjust the pads.