Hi I am trying to replace the cv boot and stuck trying to remove the hub nut it moves and gets locked, Is there a lock somewhere or something needing removing first.

Thanks

 

There a tab on the nut that has to be pride a little just keep turning should come off if wheel spins get someone to put there foot on the brake, use a breaker bar

 

Or if your alone. Put the wheel back on. Remove the centre cap and remove the nut with the car sitting on the ground

 

I had major issues getting one of mine of, had to use a 5ft long scaffold bar in the end with me literally hanging of the thing bouncing up and down, i managed to snap a 1/2 drive bar split a snap on socket an nie on break my wrist in the process lo, iv heard of people putting the bar and socket on the nut and driving the car forward to crack of the nut, i would not recommend that though lol.
As someone has said refit the wheel drop the car down to the floor, pop out the wheel center cap, fit the socket on the nut with a breaker bar and get the longest pole you can find and put over the breaker bar for leverage, get some to apply the breaks and put on handbrake, it safer this way as the car wont fall of the stand/jack, then give it all you can, be careful though as when it cracks if you are pulling down on the bar you will go down like a sack of ****.
Also when refitting copper slip/ease is your friend .