Both phrases should be written with a capital letter 'I'. Note that the pronoun 'I' is always capitalised. 'I want' is standard English, in both written and spoken forms. 'I wanna' belongs only in SPOKEN English. It is ( more or less) what 'I want to' sounds like when native speakers say a sentence like 'I want to go home' in rapid relaxed speech. We hear something like 'I wanna go home', we don't deliberately choose to say this. Some important points to understand: Unlike slang, which is a deliberate choice of vocabulary or phrasing, nobody chooses to say 'wanna'. Native speakers don't say to themselves: 'This is an informal situation, so I'll say 'wanna' instead of 'want to'. It is something that happens naturally when we are speaking. The only time when it is appropriate to write 'wanna' is when you are imitating a certain style of speech, for example in cartoon captions, movie subtitles and song lyrics. It is NOT an alternative to 'want to' in everyday written English, however informal.

"I want " is standard English. "I wanna" is slang for I want to

"I want " is standard English. "I wanna" is slang for "I want to.. " Therefore after "I want " you must add the word TO For example "I want to go swimming" , "I want to learn English". It is correct English, but "I wanna" is slang and should only be used when we speak informally and we would not write it in formal English.