What can you do to pop your ears when you have a cold?

Eustachian tube: With a cold, your nasal passages swell. This can render the eustachian tube less functional. This necessitates greater pressure difference between your middle ear and environment for the eustachian tube to open. When it does, there is a greater gust of air exchange producing a greater excursion of your ear drum. Thus, it seems to pop.