Minecraft Help? How Do I Install Texturepacks in Demo?

If on xbox or playstation: there's no folder you simply can't get them without the full game.

If on pc: I don't think there's folders for demos of minecraft. Press the start button on your lower left side of the screen and type %appdata% then open.minecraft folder. If there isn't already a resource/texture pack folder make one and put the file in there.

Well you can't do that unfortunately but you can buy minecraft.
Or go to my youtube channel www.youtube.com/user/lokesh balaji and check out a video i made in which i gave my minecraft account away.
all you have to do is like the video and subscribe if you like my videos.