Your phone must be on offmode to access recovery mode, then press and hold the volume up + the power button untill phone vibrates or light up. Use the volume buttons to move the highlighter, use the power button to confirm.
I've also notice that installing a lot of apps on internal storage couses an android phone to freeze, slow or malfunctioning of apps. Be advised to close or exit an app when done using it, you can clear recent running apps by press an hold the home button for few second and then touch "clear recent application". You must also uninstall apps that your not using free up some internal storage. I hope this helps.