Recently bought a Samsung Galaxy S4.
This is how you get into download and recovery mode - in relative safety :)
For Download Mode you press
Volume Down + Home + Power Button
To do this in an easy way do the following
Press and hold Volume Down + Home Button(the one in the middle bottom) when you have these pressed press and hold the power button until the device does a feedback vibration and let go of the power button but keep holding the other two!
When the screen asks you if you are sure let go of both and press the volume up button to accept!
For Recovery Mode you press
Volume Up + Home + Power Button
To do this in an easy way do the following
Press and hold Volume Up + Home Button(the one in the middle bottom) when you have these pressed press and hold the power button until the device does a feedback vibration and let go of the power button but keep holding the other two!
When you get into Recovery let go of the other two buttons and do your thing!
