1. You need to power off your phone first. Then, after it’s shut down, hold simultaneously the ‘Power’ button and the ‘Volume down’ button for a few seconds (if this does not work out, try with Power and Volume Up - the combination might vary across devices). Then, release them and you should see a list with options.
2. (The simplest way). If you have root access, you can simply download the free ‘Quick Boot’ app (external link) from the Google Play Store. From there on, you just select the way you want to reboot your phone (you can select to reboot straight into custom recovery), and that’s it.
3. The final method would best fit those of you who have access to a computer, and have plugged in their phone via a USB cable. You also need to have USB debugging enabled in order for this to work.
In this step, you’d need to go into the /platform-tools folder on your computer (it’s a sub-folder inside your Android SDK). There, you press Shift and right click with the mouse, then select “Open Command Windows here”
In the window that opens, you type the following: