I just pull up on both sides using my fingernails (hopefully didn't cut them that day ) in an even fashion. Never had a problem with it. There's not really any flexing or anything either that would indicate it could break.

Also make sure to put the boots on (new ones) in the right order. I put the inner one on in the wrong order and it took 2 screwdrivers, grease, and my girlfriend (kinky?) to get it off.

And finally, nice looking leather shift boot. Is that redone or original?

 

http://www.mazdatrix.com/faq/shiftbsh.htm