If the fungus is inside the lens, which it usually is, you will have to have a qualified repair man do the job. The lens will have to be disassembled, cleaned and then recollimated. One of the problems is that fungus attacks the lens coating, so removing the fungus still leaves the marks in the coating. Lenses can be recoated, but it's quit expensive. In my experience, one can buy a good used lens for less. If yours are 20 years old, they certainly aren't the latest auto-everything and generally can be found for a reasonable amount.
Store lenses in a dry place, if possible with silica gel in a big paper envelope. Note: plastic bags outgas polymers and will leave a coating on the glass that is difficult to remove and may also affect the coating.