How do I change the resolution of videos and pictures to make the file sizes smaller?

DJI Go app.. Camera Settings.

Your question implies you might not have read the manual.  If not, you really should do it.  With the large investment in your quad, there are a large number of things that need to be understood if you are to keep from crashing it or having it fly away.  Just sayin'.

Thanks to the replies above, and please go to camera settings to select the video size when you are in the recording mode, and switching to photo mode to change the image size.  

StanfordWebbie Posted at 2017-10-24 17:37
Your question implies you might not have read the manual.  If not, you really should do it.  With the large investment in your quad, there are a large number of things that need to be understood if you are to keep from crashing it or having it fly away.  Just sayin'.

I agree. I fear he will not take your advice and soon we will see a post from him such as:
"Crashed my Mavic into a wall in my living room." or perhaps "My Mavic flew away!"

Give it time.. some learn harder than others. Nice of you to advise though.

Dear Fryburger,
As some fellows said above, it is quite an obligation for a pilot to be aware of the piece of technology he is holding.
It is not a toy.
And it can be dangerous!
Just an advice.
Cheers.