Stupid Question: How to take out tubes??

Pull the tubes in an "upward/vertical" motion. Try to hold it as far down from the base as possible if you can. A soft cloth rug can help you hold the tube more solidly. If it seems that the sockets does not want to let go, use a few drops/spray of Progold and the like to "loosen" the pins friction from contact to the socket and with a pulling motion, rock it gently but not excessively.

I have never seen a tube socket with a release lever. Maybe somebody can answer you on that.

First, call them on the phone and ask them out ;) If they say no, then do the following:

turn the unit off, let any stray electrical charge dissipate, use cotton gloves or a soft cloth, pull them straight out of the socket.

I pull out the power cord, put on real rubber gloves, and pull them straight up. I got zapped once (putting a herbie halo on) so I use the rubber gloves now.