Unable to customize theme

So I’ve seen a lot of posts already saying people have had trouble being able to customize their theme.

I’m having the same problem. I installed WordPress through iPage, and then attempted to change and customize the theme of my site. I tried doing the generic themes (“Twenty Fourteen”, “Twenty Fifteen”, etc.) to see if that would work, to no avail.

When I go to the page, the left menu appears along with a gray circle that is the loading screen icon. Based on a recent post, I tried uninstalling and reinstalling WordPress on iPage. I also have tried deactivating all plug-ins. People keep talking about “cache”, but I honestly have little idea where to find or change that.

I’m not a computer expert, and I’m new to WordPress and iPage. There seems to be not one definite method of fixing this… Any ideas would be greatly appreciated!