blackhornet said one way to do it, there are several other ways too.
If you click the sprite type in the objects window on the right side of the screen it will select all of the spites, then you can delete them.
If you want to leave a few you can then hold down the Control Key and unselect some (then delete the rest).
You can also start by clicking one, then holding down the Control Key and click on as many others as you want - then delete them (or move them, or copy and paste more, etc.)
You can also use the mouse to click and drag a selection box over a bunch of sprites which will select all the ones completely inside the selection box. (but that will select anything else as well)
If you use multiple layers to organize your game you can then lock layers you don't want to change to make it easier to select objects.