Need html code to automatically refresh a page once every 70 seconds

I have a public service site that has as its sole purpose to display lightning strikes within up to 350 miles. The main company that runs the triangulation and such needs me to upload a 50k png file once a minute. It is doing that just fine. HOWEVER, ixwebhosting apparently is having some sort of difficult with this most minor of requirements. They asked me to have code inserted into the index.html page that will cause a surfer's page to automatically refresh. I do not know html. The site is VERY basic. It is www.montroselightning.com Can anyone look at the index.html page and tell me what code to insert and where to insert it? It does seem to be a lot of runaround to accomplish something that "seems" like a very easy task. I hope someone can help out. This is 100% non profit and exists solely for public safety.