You may add more users by navigating to the Account Management area: 

1) Hover over the settings icon at the top right of any AppColl screen. 

2) Select Manage Account.  

3) Click on the Logins / Matters tab. 

4) In the Matters row, enter the number of Matters you would like total for your account. If you have maxed out your matters, increase the number of users in the above column. (See Add Logins to your Account) 
 

5) Log out and then log back in to put the changes into effect.