Hi,
have a look at the Design Note 339 from Linear Technology, i attached, for a general overview how autorangeing can be realized.
In your case would need an PGA which can switch between a gain of 0,5 and 1, or a switchable voltagedivider.
Or you could use just use a fixed 1:1 voltagedivider to reduce your max. 10V to 5V and switch your reference Voltage to 1V when your input Voltage goes below 2V.
This would be the cheapest and easiest way to do it, with an 10Bit ADC and 1V Reference that would be 0.97mV per Bit.
Therefore your input voltage resolution is 1.94mV per Bit.
So you have to decide if this resolution is good enough for your application or not.