Answer:
1) Right Click anywhere on your PC's Desktop screen
2) Select Personalize
3)The 'Settings' window is gonna appear
4) On the left hand side find taskbar(click it)
5) Find 'Automatically hide the taskbar in desktop mode'
6) Click On.
Hope it helps :D
Right-click on an empty area of the taskbar. (If you're in tablet mode, hold a finger on the taskbar.)
Click taskbar settings.
Toggle Automatically hide the taskbar in desktop mode to on. (You can also do the same for tablet mode.)
