That is the spindle but. DO NOT TOUCH THAT. That holds the bearings on the spindle. Having that but to tight or loose will tear up the inner and outer bearings and seal. To get the rotor off the spindle. Soak good with pb blaster, wd-40 or what ever you prefer. With it on jack stand I always put the tire under the side of car just incase it comes off the jack stand. Use a big "rubber" mallet or a block of wood and a hammer and hit it from the back side of the rotor from on side to the other on the back to break it loose.
If you did move the spindle nutt let us know and we will help tell you how to adjust, I am changing my front bearings this weekend. 80k miles and drivers side is loose needs changed.
The front bearings are not hard to change or adjust but if you have not done it before or know how to properly pack a bearing ask for help.