I had a student today dealing with this.
First off, I was never taught how to deal with this, most of us weren't. Eventually you will be able to change quickly, rest assured. Your brain will eventually figure out the best way to direct your fingers from one chord to the next and it will be taken care of. It's that simple.
if that's taking too long and you want results sooner rather than later, try this:
Play and chord and hold it, now envision the next chord. Then GO! Make the movement quick, like a jump. Even if it's sloppy at first.
Another thing to do is changing in time. Play a chord and hold for three beats and use beat four to move to the new chord:
strum-----------------------change ---- strum ----------------- change
1---------- 2 ---------3--------4----------1--------2--------3--------4
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