I need help on guitar music "grenade" ?

the vast majority of guitarists dont remember a set strumming pattern for each song. the best thing you can do is listen to the song and move your hand to the rhythm. i am willing to bet that if you listen to several different live versions of the song that even the artist will have variation on the strum pattern, it isn't set in stone, and there is nothing wrong with putting your own unique twist on the song