On datasheet page 13, the table have one item called "Sensitivity" for acceleration sensor, you can refer to the value to convert the sensor read out value to g value.
Take example as following:
1. you set the acceleration range is 8G
2. from the table, you get 4096 LSB/g
2. you read vlaue is close to 4096, then you approximitaly get 1g output. (read_out_value / 4096 *1g)