Creating A New Account

In Insightly, click on the portrait in the top right of the page and go to "System Settings".
System Settings

On the left hand side of the page, click on "Users".

Users

On the right hand side of the screen, click the blue button that says "Add New User".
Add New User

Click on the drop down menu presented to select a Gmail account to create the new Insightly account with.
Select Account

That's it! Just test that this has worked by signing into Insightly under the Gmail account you've just made.

Giving New Account Admin Permissions

It could be that the account you created wasn't assigned admin rights when it was made. To grant them permissions, make sure you're logged in as an administrator account already.

Head back over to "System Settings" and then back to "Users". Click on the greyed out shield icon to grant them admin permissions. If this has worked, you'll get a little notification and the shield will turn green.

Grey Shield

Green Shield