I have installed plenty of casements, double hungs, bays, bows, and awning windows ...
If you are talking about replacement windows, you will need to remove your window stops on the inside to take the sashes out.
You should be carefull changing double hungs with casements because of the width.
I think you are being taking down the wrong road.
Have a window company come to your house and explain what needs be done.
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