To add to David's advice:
If you end up trying to clean haze from inside a lens/between elements, you WILL replace that haze with scratches (aka "cleaning marks"). There's really just no other way about it. In fact, the glass in those lenses is notoriously soft, especially the inner, uncoated elements.
All that being said, I have had a modicum of success taking apart and cleaning/repairing a handful of lenses. I'm not a professional by any stretch of the imagination, but I've had the fortune of 1) being able to talk to some experienced repairmen in person along the way and 2) having worked on cameras and lenses that I got for free or bought for less than what I spent on lunch yesterday.
Depending on the model of 9cm Elmar you have, you might be able to use a spanner wrench and back out the rear elements. On my lens, this is where there is some "haze," but it turns out that this haze is actually etched onto the glass itself and is therefore not repairable. The lens is still fine though, and is still perfectly able to take good pictures.
All this to say: if you want to learn, then by all means go ahead, but be very aware of the risks. And unfortunately, my 9cm Elmar (1953 chrome model) may be entirely different from yours, and I never really attempted to do much with mine anyhow!