You can also reset your kindle but keep in mind that it will delete everything on there but you can re-register and it will load whatever you tell it to load. you don't have to load everything back on there.
Any video or movies or anything like that will take up a lot of storage. so you can remove those (but it will keep it in your Cloud) and free up storage like that.
A good site to look at is this one: http://www.makeuseof.com/tag/kindle-fires-8gb-storage/, which will talk to you about freeing up your storage also and other ideas you can free up storage with.
It will take a bit to get everything off depending on how much storage you have.
took some time free up storage ,but seems ok now many thanks