It is part and parcel that DSLR users will have dust issues when you change lenses ( lens mount is opened and image sensor is exposed ).That said unless it is very serious the first thing to do is activate your camera's dust cleaning feature from the menu, this is for loose dust particles.It's basically an ultrasonic shaker but first get a big blower brush to blow away the bigger dust particles. Some will argue blowing will just blow dust somewhere else.
Also understand since you are using a high end camera and if you want to get it serviced it will be a recurring issue so get used to giving money to Nikon to support your hobby.
People want to save money so they DIY but be aware of the risks as Nikon will always advise to go to their service center.The diy effectiveness varies with individual owners and skill.First, need to test whether there is dust on sensor by shooting at white wall or paper at F22 below.:
How to clean ccd: http://www.imaging-resource.com/news/2015/04/11/how-to-clean-a-ccd-sensor
Long article by Thom Hogan: Read the legal disclaimers first.