How can I switch the time between 24 hour and 12 hour?

Start the Regional control panel applet (start - settings - control panel - regional settings)

Select the time tab

HH in capitals means 24 hour, hh (lowercase) means 12 hours

Click Apply then OK

Start the registry editor (regedit.exe)

Move to HKEY_CURRENT_USERControl PanelInternational

From the Edit menu select New - String

Enter a name of iTime

Double click and set to 0 for 12 hours and 1 for 24 hours. Click OK

Close the registry editor

Logoff and on again