The bracelet is fitted with a pin, that needs to be carefully punched out. I suggest you leave that to someone who has done it before, because it has to be done gently not to create too much shock to the movement.
Once the bracelet is off you can use (slightly curved) spring bars with the tropic, and yes, you need to order a 18mm buckle as well.
The strap change tool that came with the anniversary would be of a little help anyway, since it does not help the removal of the entire bracelet.
Hope this helps.
Cheers
Henrik