I just did this with a red cover. Came with no extras, so I had to take everything out of my old cover. Didn't take more than 30 min, EXCEPT
I put the port for the usb charger in backwards. No big deal, took it off again - The adhesive that I used for the side pieces I guess wasn't dry when I put it back together. Stuck to the side ribbon for the volume and power button and ripped as I took it out.
Not a huge deal, can get another for $11.... I would just recommend doing it right the first time, or make sure if you use adhesive, let it dry