Below are methods for testing your attention span, increasing attention span and increasing memory

Increasing Attention Span video

Concentration/attention activity

Improving Memory video

Organisation tips video

Recommended book: ADHD 2.0 by Edward M Halliwell and John J Ratey

Games to increase memory/attention/concentration: 

Memory Games - Play Online For Free | ImproveMemory.org

Free Concentration Games and Exercises to Improve Focus | MentalUP

Brain Games | Free Brain Games to Play Online (brainpages.org)