To remove the chuck, just pull the quill up, put the spindle either in high gear or low gear (lever on the right hand side of the head) while applying pressure to the hand brake (lever on front left side of head) use a 3/4" wrench to unscrew the drawbar at the very top of the head. Unscrew it about a turn or two, then take your wrench and tap on the end of the drawbar. By tapping on the end of the drawbar, you are vibrating and applying some downward shock to the chuck to pop it out of the taper fit. Make sure the quill isn't locked when you raise it up and down. The quill lock is on the lower right side of the head. It's the little lever about an 1-1/2" long.
Both the chuck and drawbar will drop slightly which will enable you to finish unscrewing the drawbar from the chuck. Make sure you have your hand under the chuck to catch it when you unscrew it. It should be an R8.
A few things to consider when selling this machine. Most people will want a good look at the ways For lack of a better description, it's the "guides" which the saddle rides on and the knee goes up and down on. You might take some pictures of that. If the ways are really good, which is rare, the machine could be worth $3K or more. You'll get the most money if they can run the machine under power.
A common mistake of friends and relatives of machinists, selling stuff like this is the tooling. They don't realize the tooling is many times worth more than the machine. For example, the keyless drill chuck in the spindle could be quite valuable if it's a high quality brand.
Also check the side door of the Bridgeport for any tooling there. Some people (including myself) keep some tooling in there. As an example, I have some good quality collets I keep in there, that I paid about $600 for.
I once happened upon a local Craiglist ad where a Grandson was selling Grandpa's machinery. He took lots of photos and was asking $2500 for a decent looking Bridgeport mill. There was loads of tooling he threw in for "free". I'd estimate from the pictures, it was about $10K in tooling. The ad didn't even last a day. I'm sure the guy's phone was ringing non-stop.