If you're rooted and/or have a custom recovery, then you can do it from your phone through said custom recovery (such as ClockworkMod Recovery or TWRP).
Rooted = having root user enabled + the SuperUser binaries that linux uses.
Not all phones can be rooted. Doing so varies from device to device. If you don't know what root even is, then it wouldn't really benefit you so I would advise just keeping your device stock.