In order to do this, you simply need to move the decimal place to the left by three places. Each time you move a decimal point to the left a single place, you are effectively dividing by 10.

The amount 2000mg, can be written as 2000.0 mg.

To convert to grams, move the point to the left three places:

2000.0 mg -> 2.0000 g (2g)

Hope this helps, let me know if you have any problems with the answer.