How to smooth out the slope between two fragments? I have a model where the curve between the two surfaces needs to be smoothed. 

The one near the left border of the red rectangle and the other on the opposite side. What I need to do, is change the angle between the two fragments. 



I think the 2nd image speaks for itself. The red line shows how it looks right now and the green one shows the effect that I'm looking for.



Does anyone know how can I achieve the desired effect?
With your mesh selected go in to sculpt mode.

Choose the Smooth brush by pressing S, then LMB  and drag over the places you want smoothed.



If you do not want to use sculpt mode.

In edit mode, select all of the vertices, by pressing A A. Then click on the button on the tool shelf, on the Tools tab under Deform: called Smooth Vertex. You can adjust the number of iterations the smoothing runs in the bottom of the tool shelf, or by pressing F6.