Nothing new here but just to reiterate, might give you a little more confidence. Everything above is correct.
You are absolutely 100% allowed to cancel an existing order at any time, for any reason up until you enter your PIN on collection. Seriously, you can cancel because you wake up with an itchy nose and saw a wierd looking cat if you want to.
As for your lease ending, it doesn’t matter when your current lease extension ends – if you have a new car on order, your current vehicle stays with you until the new one is ready to collect, so if the Volvo is what you want and the wait time is something you’re happy to deal with, cancel the Kia, order the Volvo and sit back and wait.
"Man is born in freedom, but he soon becomes a slave, in cages of convention, from the cradle, to the grave."