So do I 
But we never give up for it. If we think we can do that, everything can be possible.
If you think you have bad grammar, the first advice i wanna give to you is you must have strong will to study grammar until you can understand how to use it.
If you have strong will to study, everything will be easy to you. You can study grammar with autodidac (study in the application , browsing how to use the grammar in the sentence, watching youtube, etc) or you can take a private lesson which is teach about grammar..
After you studied it by your self, you must practice use grammar in the daily life (because it's not guarantee if you speak english fluently, your grammar is good too).
Best advice that i can give to you is don't give up to study grammar, because it will important to your life.