Your tank is less than 2 weeks old. It is not cycled so needs to grow bacteria. Do the biggest water change you safely can with the shrimp and plants you have in the tank. If you can, treat the water with excess dechlorinator before adding it to the tank because a newly established colony of bacteria will be more sensitive to the chlorine in water.
During this period do not clean your filter sponges at all unless flow rate has massively reduced. You can help the process along by getting filter media from an established tank and potted plants from established tanks and adding them in to the filter and tank respectively.
If that doesn't get your water down to 0.25 nitrite, then a few hours later do another. Because you have shrimp in the tank you will need to change the water any time the nitrite gets to 0.25. Nitrite is toxic to shrimp and will harm them. If you have an established tank that has already cycled I'd recommend moving the shrimp there. For any future tanks you should ensure the tank has cycled before you add any animals to them.
As Maq says keeping Oxygen levels up, it will help your bacterial colony process ammonia and nitrite and reproduce to establish. You can do this with airstones and pointing filter outlets at the surface to create Choppy Waves. Also by taking a jug of tank water out and pouring it in from height several times per day (that last step is really only necessary if you can't do the first two).
As a general rule with fish tank advice the more information you can give the better advice you can get. As a minimum, tank dimensions, what's in the tank and how long it's been in, water parameters and anything you're adding to the tank (treatments, fertilisers, medications).