The only word you need to change is "increase". "I want to improve my English speaking ability."
A couple of other things...
Don't ever use "wanna" in regular writing. It's the most obvious way of showing that you are a non-native speaker. Look at how native English speakers write on italki, and you'll see we simply don't use "wanna"! :)
Also, the verb "to be" takes adjectives, not adverbs. "Be correct", and "say correctly".