All you can do is jack the car up make sure it secured safely (very very safely) on an axle stand (it would be safer to do this on a 2 post lift) with the wheel in the air that's being removed (Sorry for being so obvious) and chock the wheels on the floor somehow, undo the wheel nuts (of the wheel in the air) either almost to the end to keep the wheel on after it's loose (this can depend on style of wheel as this could cause possible damage) or remove them completely but have a large old cushion or something on the floor just in-case the wheel falls of after loosening, place something under the MINI that will hold the weight should it fall of the stand / stands (old wheels, anything), then either whack the wheel from behind with a large rubber / wooden mallet (or a lump / sledge hammer with a block of wood between hammer face & wheel, normally requiring 2 hands

), moving the wheel after each blow, you should eventually notice the wheel to move / wobble as you go round, but remember to keep an eye on the axle stands all the time to make sure your MINI doesn't slip off, sometimes the wheel can just go at any time and other times they are stubborn to the very end, so depending on how you've done it once loose the wheel bolts will hold the wheel on, or once it's partially loose try to pull it off yourself noting if the bolts are on or off and remove them when necessary, worst case they fly off & fall on the floor, face down you normally can't do nothing as you have an hammer & block of wood in hand :aargh:, hence the cushion etc... etc....
Please remember people have died doing stuff like this so I can't stress how important it is to make sure the MINI is secure, make sure if it does fall off the stand / stands it has something to fall on & not you, and keep your eye on the situation as you go be ready to move fast, if possible have someone with you either to assist with the wheel or help should anything happen

.
To prevent seizure in future use copper grease on the bolts / nuts but also only very lightly grease the centre of the wheel and mating face where the wheel meets the disk remembering not to put so much on that it spins off when in motion and contaminates the brakes in any way :aargh:.
Sorry for being so very very obvious but as I said people have died doing stuff like this and the brakes issue is just as important and I don't want anyone misreading / misunderstanding this post and attempting to knock a wheel of while under the car :aargh:.
I have had to use a sledge hammer in the past in the worst cases, and that's all they'll do if you go to a garage or tyre fitters, although they'll have the safety of a 2 post lift.