"want to" is the standard use. "wanna" is a lazy way of saying it. It is frowned in writing. Used mainly by the uneducated or those of unsavory background. Same for "gonna" vs "going to".

Wanna = want to

Hola. Como estás? Want is proper English. Wanna is slang. They mean exactly the same thing. Do you want to eat cereal for breakfast? Do you wanna eat cereal for breakfast? In any kind of formal writing you always want to use the first.