I am upgrading to a iPhone13 pro
Do I transfer the sim card from my old phone to my new phone?
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Of course.
First make a complete backup to computer, not only iCloud. See the difference Backup methods for iPhone, iPad, and iPod touch - Apple Support
Then do this Use Quick Start to transfer data to a new iPhone, iPad, or iPod touch - Apple Support
When it's done, mode the SIM card to the new iPhone and it will now be your main phone.
For the old phone, make it clean so you can sell, give away or recycle it What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support