This is likely to be down to the browser cache. When you view a webpage in your browser it, and the resources on it, will be stored in the browser's cache memory. The next time you view the page (which is usually unlikely to have changed very much) the browser will use the cached data instead of downloading it in order to make the page load faster.
If the content of the page is different to the one in the cache then you will sometimes just see the cached page, the new page, or a mixture of the two. In order to see exactly what you should be seeing you should refresh the browser (the shortcut for this is usually Command-r).
If this isn't the cause of the problem then make sure you are uploading to the correct directory as specified by your web host. You will need to refer to their documentation/correspondence or contact them to find this out.