I'm not familiar with the Z390 or which version of Android it is running. However, it seems that you need to be rooted to do it.
From an earlier answer:
"Unless you are rooted, I don't know of any way to do it. If you are rooted, or are willing to root your Galaxy for those nice guy points, you should be able to use a file manager (ASTRO, Root Browser, etc.) to find it.