Whenever I start Hugs, it always says
Haskell 98 mode: Restart with command line option -98 to enable extensions
How exactly do you do that?
If you're launching it from a command-line (Bash prompt, Windows Command Prompt, or the like), you would just change your command from ... to ... -98. (For example, if you've been running the command haskell, you would now run the command haskell -98.)
If you're launching it from a shortcut icon in Windows, such as a start-menu item, you have to modify that shortcut: right-click, select "Properties", and change "Target" from ... (whatever it is now) to ... -98 (whatever it is now, plus a space, a hyphen, and ninety-eight).