Open Instagram
Go to your profile
Tap your followers count
Find the follower you want to remove
Tap Remove next to their name
Confirm Remove
If the account is private, remove followers from your followers list
If the account is public, block the person to stop them from following you
To block someone, open their profile
Tap the three dots
Tap Block
Confirm Block
To limit future followers, switch your account to private
Go to Settings and privacy
Tap Account privacy
Turn on Private account