Reedit: Using these instructions, you can switch a survival map to creative:
- Download NBTedit from here
- Unzip the ZIP file
- Run NBTedit
- Click File -> Open
- Navigate to your save folder
- Save and exit.
In multiplayer, ops can type
/gamemode [playername] [1 for creative, 0 for survival]
Edit: This is wrong! There is a /fly command you can use! same controls
If you use "Single Player Commands" you can:
- press "T" to open the Console
- Use the command "/noclip" to allow you to fly around, however you can also "Fly" through blocks,.
Controls for /noclip flying:
WSAD: Move like normal
Shift: Go down
SPACE: Go up.
This isn't really "flying" in the sense that the Original-Poster meant but you are flying!
Edit: This is for Single-Player, not Multiplayer. Hopefully this will help someone who wants to fly in single-player but I don't think it works on multiplayer.