You should first ask a teacher to listen to you speak for a few minutes, and list for you every sound which you articulate in a non-standard way. This is not about accent, but about standard pronunciation.  

You should then work on eliminating all those non-standard sounds, starting with those which most affect your ability to be understood.  

You should also continue to improve your English to C1 level. At that point, you will be very fluent and can consider more seriously the issue of selecting a particular accent.  

In my experience, most advanced non-native speakers of English don't focus on accent, but there are some who have special reasons for doing so.