To modify multiple tickets, first run the query that will put them all on the same screen. For example, issue a search for incidents (or other ticket type), with Status=Open.
Once the tickets you want to update are in a list (click List All on the bottom where necessary to display a large list), click Edit in List.
At first, the Save(@) button is not enabled. Make the desired changes, for instance by changing the Status field from Open to Closed.
The Save button is now enabled. Click it, and all items in the list are updated.
On using "Change All"
There is also a function that you can use, called "Change All". This will make whatever change you are attempting apply to all entries in your search result:
In the above example, we see that a status change of "Hold" has been applied to Request #44. If one were to click on "Change All", this will apply the same change across ALL search results depicted. It will not differentiate across entries and will apply the change equally across all search result entries. However, the update will not take effect until one chooses to "Save". "Change All" only sets up the result-scope update being made.