[kcstengelsr]

to aceshigh,

at top of screen click Game and then click Game Settings in the dropdown.
next click on League Settings.
see the three sections, scroll down the middle section to Set All Computer Teams to Allow Roster Changes. clicking on this sets all teams to be run by AI. also notice Set All Teams to Not Allow Roster Changes. if your teams are currently running on AI this forces all teams to be unable to make AI roster moves if you click on this.

Another way if you want just one or some teams to be affected:
Let's say that you want just a few teams to have set rosters with all the others making AI moves.
click on any team
click on settings from that team's page
scroll down the left hand side of the split page section to Roster AI and note the checkbox for Prevent Any AI Roster Changes. if the box is currently unchecked you can click on the box to prevent any AI roster changes for that particular team. if the box is currently checked you can click on the box to uncheck to allow AI roster changes for that particular team. this is helpful because let's say you are tracking a particular team but don't wish to GM and want to see how they do with their current roster and you don't trust the AI to make roster alterations like promotions and demotions. you can set that one team to not make AI moves but if you have enabled injuries you typically will be forced eventually to make some changes. you could then click on allow AI moves to adjust for said injuries and if you like those you could then go back and reset the team to not allow AI moves again.