If you are using Instagram version 7.15 for iOS and Android, you will now have the ability to use multiple and switch accounts. The feature allows a user to add and switch between IG acccount without logging-out an account. You can add up to 5 user.

Instagram also posted this on their Help Center for a step-by-step instructions on use the new feature.
Instagram Switch Account

The multiple and switching of IG account will roll-out to Instagram users starting this week. No doubt, that this is great news for users who manages multiple accounts like brand and social media managers. You can read Instagram’s the official announcement on their blog.