uploading media to slider on theme

Hi, I am having real difficulty getting any photos to show up on a slider I am using with the WP theme I bought. I have changed the sizes of the photos mulitple times, but still when I hit browse and choose the photos, and then “update” it’s taking about 5 min to even upload (to bring up the little screen with the photo that was uploaded and the options with it). And then after I had all 4 sliders done, with different photos, the photos are not showing on my site….just showing an empty box, with the slider dots moving, but no photos. I called my host company, and they had already optimized my system, so they are not sure what is going on. I would be very grateful if anyone could help? I appreciate any info. Thanks much.