Nxtgen Nav-prev and Nav-nxt NOT showing up

Hi! can anyone help me.

I have installed the nextgen gen on my wordpress site. and i notice that the arrow (nav-prev; and nav-next) are cannot be found. it has a broken image on my site.

also, tried to fix it, and it says that the file (the jpeg file) are not found.

can you help me on how to fix this.

Thank you and looking forward in hearing from you.