I guess.Int32.Parse will do it too... but you have to assign the numericUpDown value to string, this is becuase value of numericUpDown`s control is in general a decimal vlaue. So parsing to string is needed.
So you have to do:
//to get the directly the value from numewric, you have to create decimal variable:
decimal aa = numericUpDown1.Value;
int bb = int.Parse(numericUpDown1.Value.ToString());
//and as said:
int cc = Convert.ToInt32(numericUpDown1.Value);