Clean the pen so that no ink will stain your hands or clothing during the nib-changing process. Use water and paper towels to remove any encrusted ink. Spread paper towels over the work area to catch any ink that may flow out during the nib change.
Hold the pen over the paper towels and grip the old nib as it sits in the pen. This can be done in a number of ways, depending on the brand of the fountain pen. Some pens, such as the Papershow brand, have a small hole in the clip on the cap of the pen into which the nib's point can be inserted, creating leverage.
Grip the nib in another way if there is no built-in method. For example, pens such as the LAMY do not have leverage holes in the clips. In this case it is sometimes helpful to use the sticky side of clear packing tape to grip the nib.
Slowly but firmly pull the old nib out of the pen. Discard it if it is too worn to be used further or if it is broken.
Align the new nib with the pen so that the convex curve of the nib coincides with the top of the pen barrel. Push the nib firmly into the pen to seat it. With some pens, such as the Papershow, you can use the hole in the clip for leverage in seating the nib.