Ideally, that face should reassemble a grid made out of quads (polygons of 4 vertices) so that when you sculpt it, the resolution is more or less equal along the entire mesh
The fastest way to do so would be to delete that big face on the middle, selecting the edge loop (Alt+Click) corresponding to the face you just deleted and in the face properties menu (Ctrl+F) selecting the option "Grid Fill". If the results are not what's expected, in the redo menu (the small popup that appears after you perform an action on the bottom right of the screen) are some options to adjust the algorithms response.
In classic stackexchange/overflow I will refer you to an older question and the manual that explain this exact function in a more graphic way.
If you are a beginner this is the simplest yet more correct way i can think of to set you up and running. As you keep learning you will probably need to find more appropriate ways to correctly preparing your mesh for modelling or whatever,providing you with the best results. One step at a time.