The settings can be changed behind the information poster in the lobby. You have to be in creative mode and have OP rights. With „+“ the setting is increased, with „-“ it is decreased. In addition, the possibility to play in freeplay mode can be switched off.
Alternatively, the settings can be set by command:
/scoreboard players set xxx settings num
Replace xxx with the internal name of the setting, replace num with a valid number.

These settings exist:

NameOptionsInternal Name
Maximum Number of Players4-10max_player
Number of Impostor1-3impostors
Confirm Ejects0-1 (off/on)confirm_ejects
Number of Emergency Meetings0-10emerg_meets
Anonymous Votes0-2 (off/on/special)anonymous_votes
Visual Tasks0-1 (off/on)visual_tasks
Emergency Meeting Cooldown0-60 (in steps of 5)emerg_cd
Voting Time30-210 (in steps of 30)vote_time
Player Speed1-3player_speed
Kill Distance0-2 (Short, Medium, Large)kill_distance
Kill Cooldown5-60 (in steps of 5)kill_cd
Common Tasks0-2common_tasks
Short Tasks1-7short_tasks
Long Tasks0-9long_tasks
overview of the setting options