It's hard to actually give you a working example from the code you provided above, but I went to Nivo Slider's page and played with one of their demos in the console. What you can do is change this:
/* Control nav styles (e.g. 1,2,3...) */
.nivo-controlNav {
text-align:center;
padding: 15px 0;
}
to
/* Control nav styles (e.g. 1,2,3...) */
.nivo-controlNav {
text-align:center;
padding: 15px 0;
position: absolute;
top: 800px; /*CHANGE THIS VALUE TO FIT YOUR NEEDS*/
left: 200px; /*CHANGE THIS VALUE TO FIT YOUR NEEDS*/
z-index: 5; /*MAKE THIS HIGHER IF THE BUTTONS ARE NOT ON TOP OF THE IMAGE IN YOUR
EXAMPLE, THIS WAS ENOUGH ON NIVO'S SITE*/
}