I recently discovered how to use them but i wanna change the image associated with the folder how do i or where do i go to buy images?

you cant

Please do not give out false information.

Den Folder Backgrounds can be found in Monthly Event Shops and are bought using the current event currency.

Thank you

oh sorry :C

i made a mistake

You can also unlock a new den folder image each time you unlock a new explore biome (every 10 levels reached in explore)