Changing order of newsflash items
As a general rule, when you create a new article item - the newsflash module will display this on top. But it does not make this decision based on the date the article was created or modified, it makes this decision based on the order in which the articles appear.
By default a new article is "ordered" on top (first) on the list. The newsflash module - puts things in order of the ordering, not the date created or modified.
So if you want to change the order in which a newsflash is presenting information - go the backend (administrator), go to content / articles / then filter your search (using right hand drop down) according to the corresponding section or category that the newsflash module is drawing from.
Order your items in the way that you want them presented.