Heroes gain the ability to reset their abilities after changing class. This is a one-time opportunity that can be delayed but is never regained. Press the Respecialize button to unlearn all abilities of the hero located on the Might tab and the Magic tab. Regained ability points can be used to learn different abilities.
I think it means you can change from blood to tears. During the 2nd necro map, I went blood til 250 points then I started going tears. I almost made 1000 tears points which would have bumped me to the 2nd level of the tears path. I'm assuming that's when you can re-specialize.