Hello again Marina,
To be able to better help you could you please share your system information with me? Thanks!
Can I ask what version did you update from? Not so long ago we have changed how tickets and ticket stock is handled.
If this is the case then the following article will probably answer most of your questions:
https://theeventscalendar.com/knowledgebase/making-tickets/
To give you a short answer on how to change global stock:
Global stock has been renamed to “Shared Capacity”. You can set up the shared capacity when you click on the “Settings” button in the ticket section (screenshot) which will open this form where you can enter the desired value.
Hope this will help you get started. Let me know if you have any further questions.
Cheers,
Andras