The motor assists up to 28mph. In other words if you hit 28mph the motor shuts off. That is to keep the bike legal. If the motor were to assist past 28mph, then it would be classified as a moped and be subject to additional things like headlights, turn signals, brake light, and so on.
Having said this if you want to hit 28mph with the Lectric here is how. Be aware that you will likely be ghost peddling unless you are amazingly fit
1. Be sure the battery is fully charged and the cells are balanced (once the green charge light comes on, keep charging for an additional 4-5 hours, the battery manager will balance the individual cells during the extra hours)
2. Use a tire pressure app to enter tire size, rider and bike weight and pump tires to the advised pressure.
3. Lower your handle bars as low as you can tolerate
4. Raise your seat as high as you can tolerate.
6. Wait for a day with no wind or maybe even hope for a tailwind
7. Find the flattest (or downhill), smoothest, uninterrupted asphalt or concrete path of at least 1/2 mile.
8. Set bike to PAS 5. (I assume you've already done your set up mode P6 to 22 and P8 to 45).
9. Start peddling, once you are in highest gear and reach 16mph, lower your head and shoulders as low as you can tolerate (getting aerodynamic) and continue to peddle even once you no longer are making any contribution (ghost peddling).
10. Have fun while it lasts and see your fully charged battery go to 90% in just a few minutes of fun. You usually only get a single shot before the battery gets too low to provide enough energy for a 28mph run.