All that is required to become an optimist is to have the goal and to practice it. The more you rehearse optimistic thoughts, the more 'natural' and 'ingrained' they will become. With time they will be part of you, and you will have made yourself into an altogether different person.
The How of Happiness: A New Approach to Getting the Life You Want (ed. Penguin, 2007) - ISBN: 9781101202807