Finally: Account Switching on Instagram
Account Switching: Now Available on Instagram Starting this week, you can quickly and easily switch between multiple accounts on Instagram!
Go to your profile settings to add an additional account. From there, tap your username at the top of your profile to switch between accounts. Once you have multiple accounts added, you’ll see your profile photo appear in places throughout the app so you can always tell which one you’re using at the moment. To learn more, check out the Instagram Help Center. Account switching will be available as part of Instagram version 7.15 for iOS and Android.
Source: Instagram Blog