If you've found your server is capable of handling more players, you can increase the slot limit to hold more. Our support team happily will provide an estimation for you if you're not sure, judging from the package, plugins, worlds and player count. We do not limit the slot value at all as we believe that the customer should be able to decide how to run their server without wasting money if they find a larger plan not needed.
Select the server you want to edit the slot limit of from the panel.
Open the file manager and choose the "server.properties" file and scroll down to the "max-players=" part.
Set the value you want or have been informed the server is capable of.
Save the file and restart the server.
NOTE: Setting the limit to too high of a value may overload the server if enough people join and the server is not capable of that amount.