There is a limit assigned to each service level of the Adobe Sign account.
Once you reach the limit, there is no option to increase the transaction limit.
If you need to increase the transaction limit, you need to upgrade the service plan.
Let us know if you have any questions.
How do we upgrade the service plan? Currently on a Teams CC account with 13 users and each user subscribed to Acrobat Pro DC.
Sorry for the delay in response.
As you have mentioned above you have the CC teams account.
In that case, you will need to purchase either a business or an enterprise subscription of Adobe Sign to increase the transaction level.
For more details, please refer to this link Adobe Sign – Plans and pricing for enterprise and individuals | Adobe Document Cloud