Instagram users on iOS and Android now have the ability to add up to five different accounts and switch between them. The social media app had tested the account-switching feature for Android in November and last week tested that of IOS.

Instagram users who updated to version 7.15 of the app will find an “Add Account” option in the app’s settings. Once you add a second account, you’ll be able to switch to it quickly by selecting it from a new menu at the top of your profile page. Whenever you get a push notification, you’ll also be able to see from which Instagram account.
Before this update, people could not store multiple Instagram account logins at the same time. If you wanted to switch between accounts, you had to log out of the current account and log back in under the different credentials. It seemed that Instagram really wanted people to maintain only one Instagram identity, but as the photo-sharing app became more prevalent, the need for multiple accounts also grew. People who already had a personal Instagram account perhaps wanted to start another one for their small business, or they were tasked with maintaining an Instagram profile for their company or brand.
Source http://www.timigate.com/2016/02/instagram-now-lets-you-add-and-switch.html#more