Go to your Instagram profile and click on Edit Profile.
Enter the Email address you wish to use for login (and make sure you have access of this email), set a Username (you can use your username instead of email id with password to login your account).
Now go to https://www.instagram.com and tap Forgot? next to Password on the log in screen to reset your password:
- To reset through your email address, tap Username or Email, enter your username or the email address you used to create your account and tap search. Choose Send a Password Reset Email.
- To reset through Facebook, tap Reset using Facebook. You may be asked to log into Facebook. You can then enter a new password for the Instagram account that was most recently linked to your Facebook account.
Note: If you can't access the email you registered with and you didn't link your Instagram account to Facebook, we're not able to give you access to this account.
After resetting your password you can disable you Facebook account or you can unlink your Facebook account from Instagram first and then disable your Facebook account.