To change your game type simply type the command "/gamemode survival" or "/gamemode creative".  Changing this setting will effect all players on your server.  Unless... you select individual(s) who you want to be subject to survival mode, or rule with the powers of creative mode 

To do this, type "/gamemode username creative" into your commands and fill the word "username" in with the username of the person you wish to play in creative mode.  In this example the word "creative" is also interchangeable with "survival".  The choice is yours!