Stuck at Q50-How to move to Q51?

I have taken the GMAT twice and scored Q50 on both occasions. I am desperate to move to Q51 as ive read that this might improve my overall score by 20 points. Can the experts guide on how to do this? 2 options that I am confused about: 1. GMAT Club tests-These offer a plethora of tough questions. 2....