How does mass change with speed? [duplicate]

While reading a textbook on Physics, I came across this :

Mass is a universal constant. It does not depend upon the position of the body on the Universe but it changes with speed of the body.

It's just two contrasting statements with no further explanation. Maybe the author left it to our curiosity but I can't even find out how mass changes with time. Thanks P.S : This is not a homework question.

marked as duplicate by Gert, John Rennie, Emilio Pisanty, Kyle Kanos, ACuriousMind♦Nov 10 '15 at 16:54

However, you should think of this as a deprecated concept that most modern physicists consider unnecessary and misleading. Nowadays, we prefer to think that the force-acceleration momentum needs to be rephrased to something along the lines of $$\mathbf F=\frac{\mathrm d}{\mathrm dt}\left[\frac{m_0\mathbf v}{\sqrt{1-v^2/c^2}}\right],$$ with an invariant mass $m_0$, than to introduce a variable "relativistic mass" $m_R=m_0/\sqrt{1-v^2/c^2}$ in an attempt to clean up that relationship and make it look more classical.