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When the plant is done blooming you can cut it back to free it from the pot.

Pruning can help the plant.

Here is a link with more information.

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm

Yellowing leaves can indicate a watering issue, to much or to little.

Proper lighting and even insects can also be causes.

Here is a link to refresh you on the care requirements.

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm

They are usually grown indoors unless you live in a warm climate. If temps fall below 50 F., they should be overwintered indoors. This article should help you with its care: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm

Yes, you will need to move them to a location out of the winter temperatures.

Here is a link with more information.

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/winterizing-mandevillas.htm

They don't keep their Blooms throughout the Winter. They go into dormancy during the Fall, and if you try and keep it from going into a Dormant Period. You won't be seeing any blooms throughout the Winter, even if the Foliage is growing.

Your plant is beautiful.

Unfortunately your Mandevilla will not survive in temperatures below 50 degrees F.
Here is a link with more information.

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm