Hi @deset
This thread contains some code to replace the URL with the PATH:
http://wordpress.org/support/topic/full-path-to-attachment-images
You could use this in combination with the get_field() function to:
1. Get the ACF value
2. If the value is an array or ID, load the URL
3. Use the function (in linked thread) to replace the URL with the PATH
4. echo the result of the function
Thanks
E