Only one in ten people in the UK today are claiming to be happy in their job. Of course, most will do nothing about it. The fact that you've got this far at least indicates that you're considering or may be ready for a change.
It's advisable to get some help before you start - find someone who knows the industry; an advisor who can get to the bottom of what you'll like in a job, and then show you the training programs that will suit you: