I tried using 0.33uF,0.1uF capacitors and the 7805 regulator to measure +/-5V in simulation but the 5V LED is not lighting, are there any alternate values which I can use? I also wanted help on how to measure 6v when using a 5V power supply.
Is your '5V power supply' the output of the 7805, or something else. You need to clarify your request and post a schematic of the circuit you are using.
first of all, with the LED across the output like that without a current limiting resistor, you're going to get a shorted LED, and possibly a shorted 7805 as well....
many digital panel meters are powered by +5V, but have measurement ranges of up to +/-1000V. the supply voltage has nothing to do with the measurement range.
A lot of the the inexpensive Digital Voltmeters cannot measure their own supply voltage. On the cheap meters, there can be no common connection between the negative terminal of the voltage they are measuring and the negative terminal of their own supply voltage.
If your meter can measure its own supply voltage (the more expensive digital panel meters work that way), then you can use a voltage divider (two high value resistors) to read a voltage higher than 5V.