I need to replace the batteries in my 2 iPhones what do I do?

Sandra ..

Apple can do that for you > iPhone Battery & Power - Official Apple Support

See: iPhone Battery & Power - Official Apple Support

Contact Apple Support and make an appointment to have them changed. iPhones are not user serviceable devices.

Depends what phones. Apple has discounted battery replacements for these devices and your phones may be eligible for these.
[Edited by Host]