Open Instagram and go to your post
Tap the three dots on the post
Tap Edit
Tap the music or audio option
Remove or replace the song if the option is available
Save the changes
If the post is a Reel, open the Reel
Tap the three dots
Tap Edit
Remove the audio if Instagram allows it
Save the Reel
If Instagram does not allow removing the song
Delete the post
Re-upload the post without the song
If the song is part of a Story
Open the Story archive
Delete the Story
Repost it without music