Sounds like you are using a unipolar range, and you want the bipolar +/- 5 volt range. You need a request to set the range of that analog input channel to bipolar 5 volts. You can see this in the pseudocode near the end of Section 4.3.3 of the UE9 User's Guide.
In the stream example, add the following request to the Start_Stream sequence. It can go anywhere before the GoOne call, so just make it the first line of the sequence:
Device.LabJack.AddRequest(Var.d_number,"LJ_ioPUT_AIN_RANGE", 0, 3, 0);
This is saying that you want to set the AIN range, on channel=0, to value=3. You can see from the labjackud.h header file that 3 is the constant for bipolar +/-5 volt range (LJ_rgBIP5V=3). You should be able to use the string LJ_rgBIP5V, which is more readable, but this does not work in older versions of DAQFactory so just use 3.