Like all computers, the Apple iPhone occasionally
needs a reboot. You can do this by giving it a "soft
reset ". This does not remove app, songs, contacts
or anything else stored on your iPhone. It basically
just reboots the phone without following the normal
shutdown procedures.
There is different procedure to do a full "hard reset "
and this will remove everything and restore your
iPhone to its factory settings.
Both procedures are outlined below.
Method One of Two:
Soft Reset
1
Press and hold the Home button (big circle below
the screen) and the Sleep/Wake button (on top
of the iPhone) simultaneously.
2
Continue holding both buttons until the iPhone
shuts off and begins to restart. This will take
anywhere from 10-20 seconds.
Assuming your iDevice isn't totally crashed
and unresponsive, you will be offered the
ability to power off at this point. If you take
that option, remember to turn your phone
back on when you are done. Alternatively,
you can ignore the power off request and
continue holding continue following the steps
below.
3
You may let go when you see the silver Apple
logo. You have now completed the soft reset
successfully.
4
Don't be alarmed that it takes quite a while to
load from the Apple logo to the main screen. This
is normal.

Method Two of Two:
Hard Reset
1
Go to "Settings"
2
Select "General"
3
Scroll down to select "Reset". Here you will have
various options, the main ones being:
Reset All Settings
Reset Network Settings
Erase All content and Settings
Selecting "Erase All Content and Settings"
is what constitutes a Hard Reset. Your
phone will ask you to enter your passcode,
and will then ask to confirm.

Soft Reset Recommendations
It is recommended to carry out a soft reset
when your phone starts presenting peculiar
behaviour, as this clears the phone's memory
and can solve many minor problems. Some
people recommend a soft reset regularly. Some
poorly written apps or ones that crashed can
leave things in the phone's memory, and this
action clears them out. Powering off the iPhone
is similar to the soft reset but not quite as
effective in clearing out the phone's memory.

Hard Reset Warnings
"Erase All Content and Settings" will do as it says!
Make sure you have backed your phone up to
iTunes or iCloud before doing this if you are
intending to restore it afterwards.