to decrease the voltage

hi i am using a some mobile charger its voltage is 5.6 dc i want to decrease it to 3.6 plse explain me how to decrease the voltage

Using a 3.3v regulator or DC to DC converter

https://www.pololu.com/category/131/step-down-voltage-regulators

With a 3.6V regulator or buck-converter.

Of course if you think this is the way to charge a lithium battery, you are wrong. Best to explain what you actually want to do...

You need a [u]voltage regulator[/u].

The Arduino has a 5V regulator and a 3.3V regulator on the board. You can power the Arduino with between 6 and 20V, and the voltage regulators keep the voltage to the chips constant.

A basic "linear" voltage regulator chip just needs a couple of capacitors to make it a functional circuit.

3.6V will be hard (impossible?) to find, but there are "adjustable" regulators where the voltage is determined by two resistors.

Voltage regulators need "room to work". That is, if you have a 3.6V regulator and you feed it 3.6 or 3.7V it will "drop out" of regulation... You'll get less than 3.6V, and the voltage may not be stable. With 5.6V, you might need a "low dropout" regulator.

Linear regulators dissipate heat/power based on the voltage dropped across them, and the current through them. (Power in Watts = Voltage x Current in in Amps.) So, you have to be careful about the current rating... A 3.6V voltage regulator rated for 1 Amp regulator might overheat and shut down at 1/10th of an Amp if you feed-in 20V, especially if there's no heatsink.

P.S.

Of course if you think this is the way to charge a lithium battery, you are wrong. Best to explain what you actually want to do...

Good Point!!!!

MarkT: Of course if you think this is the way to charge a lithium battery, you are wrong. Best to explain what you actually want to do...

I am not sure why it is so bad idea? I thought lithium batteries are charged by limited voltage (after limited current phase). 3.6V is possibly too low but...

Smajdalf: I am not sure why it is so bad idea? I thought lithium batteries are charged by limited voltage (after limited current phase). 3.6V is possibly too low but...

Lithium batteries can catch fire if they are not charged properly.

The Samsung Note 7 recall (both of them!) weren't that long ago. Check the issue out yourself.