All the tutorials I find refer to a seemingly nonexistent “Edit Hair” button, for sculpting hair with various options. I cannot find it under any of the menus, and none of them elaborate.
I use 2.5, most tutorials are for 2.4 and are hard to use with the new GUI.
An excerpt from a tutorial:
Change back to the Particle buttons.
Click on Set Editable in the Particle System panel.
Change to Particle Mode.