Error on New Site

Please help. I am getting this error every time I make changes:

Warning: Cannot modify header information – headers already sent by (output started at /home/mpcontac/public_html/stressfree/wp-content/themes/redify/functions.php:501) in /home/mpcontac/public_html/stressfree/wp-includes/pluggable.php on line 876

I also can’t upload any media file. When I do it just shows an error for uploading.

My site is https://ronitaneal.com/stressfree/.

Looking forward to your assistance. Thanks!