Thanks Ron but I seem to have different light.... no obvious screws other than what holds the whole thing to the mast.
In the on-line pictures I have, the middle top unit seems to slide out , then the top comes off. My problem is when I squeeze what looks like the two spots designed to grip, I get no motion at all. I tried to paste an image of it on this but it seems I can't. It seems to be a Hella 62248 light

Going on Catalina Direct, I see they have an exploded view of what I have and it appears that squeezing the two sides should get the lower part out. Maybe I have to try this after I get an arthritis shot for my thumb joint so I can squeeze harder??? Their description says to simply squeeze it.... should have checked there before posting... Thanks to those who responded.

Should be a simple process but... step by step.

I got the housing between the steaming light and the deck light off. There are indentations on either side of the housing that you are supposed to squeeze but I found you have to grab the housing as far down on the edge of the housing to get the clips that hold it in place to release. Then giggle it a bit.

The next problem is to remove the steaming light lens. The directions say to push up on the trapezoidal button on the bottom of the steaming light unit (that becomes exposed once the housing piece is removed). I pushed this up but can't get any movement on the steaming light lens. The directions don't indicate if the lens should slide up, down, be pulklled straight out or tilted up... any suggestions?

Update... finally!!

Got the lens off... here are the details... 1st you have to remove the cover/shield between the top steaming light and the fore deck light.  There are indentations that you are supposed to squeeze on both sides to release the cover but, as you can se from the picture, there is a plastic "rod" going from one side to the other right about where you'd expect to squeeze. You have to get really close to the mast for the pressure points to release the cover.

Once off, there is a button on the bottom of the steaming light that needs to be pushed upto release the light lens. The lens should release from the bottom and swing up. However, I found, unless you have very short, stubby fingers, you can't get enough pressure parallel to the mast to release the catch. I tried pushing with a screw driver but that puts pressure on the button on an angle.

My solution was to use a fairly thick allen wrench (see 2nd picture). I have a set in which the larger sizes have a fairly long extension which allows holding onto it while pushing up. This popped the lens off.

Be forewarned, the lens seemed to pop off, not swing out. If you are doing this with the mast up and aren't ready for it, your lens might go swimming with the fishes.

Now to get the new bulbs and see how easy it is to put it all back together.

PS: If you need to deal with Hella, you'll find they list their New Zealand address & phone. ... thanks for that Hella. They have a Georgia address but don't list a phone.I was able to get their number from a marine contact (707)631-7500 if anyone needs to reach  them. The have a marine tech guy & he returned my call and was   helpful

Regards,

This is my last post on mast lights.. I promise. The deck light should be the easiest to replace because it's exposed and, in my case missing anyway. But try to find the right replacement bulb. 

Finally, after speaking to a Hella rep again, I found that if you Google 998529001 and Hella, you will find various suppliers of the bulb, but not cheap... $50 on Amazon.

Now here's something that might be of interest to others. In my communications with sailors in my club, I mentioned I was going to replace the mast lights with LED's (The one I reference is not but I rarely use the deck light so power draw is not a concern).

However, this caused some to alert me to the fact that they are finding LED lights are interfering with AIS and VHF functionality. The following link will take you to a Coast Guard alert about this problem. They are also looking for feedback/reports on this issue.

I hope this info proves useful. 

Regards,
Chuck Parker

https://panbo.com/uscg-warns-about-led-lights-interfering-with-vhf-ais-wants-test-results/