How to change the voltage polarity in an inverting amplifier?
There is a calculator on this website here. Here are the results for the two scenarios of: -


input voltage = -10V, o/p = 0V 
input voltage = +10V, o/p = +5V




I've arbitrarily chosen R1 to be 1K and I knew from experience that V2 needs to be half the range of the output requirements so I set that to 2.5V. By simple examination of range of input voltages to range of output, the gain has to be 0.25.

As you can see, both scenarios produce the same result of R2 = 250ohms, R3 = 1kohm and R4 = 250ohms.