If you are trying to learn English, you may ask yourself how often you should study. The answer is simple, and exactly what you are expecting. You should study every day if you want to improve in a language.
We have a saying in English. «If you don’t use it, you lose it.» This saying is absolutely true. When I was in college, I studied Japanese (almost) every day. My Japanese was near-advanced in just two years. Of course, now, my Japanese in horrendous because I haven’t practiced it in many years.
The same applies to English. Showing up to a couple lessons a week isn’t going to make you fluent in English. You must study every day. Refresh your mind every single day. Make it a goal to study for at least twenty minutes every day.