The /gamemode command can change the gamemode. "/gamemode creative" and "/gamemode survival" will work to change the mode. In Java Edition, users can also change the game mode to Spectator.

After the chat bubble appears enter /gamemode 0 to change to Survival mode, /gamemode 1 to change to Creative, and /gamemode 2 to change the mode to Adventure.

Changing gamemodes in Minecraft might be considered cheating in some cases, but it can allow players to do a variety of things mid-game.

Here's a guide for how to switch your Minecraft world from Survival to Creative Mode for Consoles, PC, and Pocket Edition.