How can I get more citizens to educate themselves?

Increase the number of jobs that require high school or college education, and make sure they pay more than the uneducated jobs. Beyond that, it takes time.

According to my personal experience and this thread, Tropicans with high Intelligence are more likely to go to High School or College. (It's factored into the "do I educate myself?" equation.)

So, if you have empty education-required jobs, and those jobs pay well enough to tempt a normal Tropican, and nobody's volunteering for education, then give up on the current generation and educate the next one: set your Grade Schools to Spelling Bee Contests to get the largest possible boost in Intelligence for your young graduates.

One of the other ideas in that thread I linked is to start a eugenics program: simply ensure that only highly-intelligent people are living on Tropico. (Children have the same qualities as their parents, so intelligent parents make for intelligent children.) Your military and secret police probably have some good ideas on how to arrange that. While you're at it, you can select for low courage, to keep rebellions down.