Browsers cache things they download, so if you look at them again, they don’t have to download all that content again – because normally pages aren’t changing.
When you do make changes to a page, you’ll need to wait a long time, or let the browser know that you would like it to download everything again completely. You do this by “clearing the cache” in the browser.
It’s a bit different in each browser, but if you Google for it, you’ll get good instructions: https://www.google.com/search?q=how+to+clear+browser+cache&oq=how+to+clear+browser+cache&aqs=chrome..69i57.7223j0j7&sourceid=chrome&ie=UTF-8