Lag in upload to website?

I have a very basic level of understanding when it comes to websites.
Have enough knowledge to get me through dreamweaver and produce a pretty simple site.

The problem:
Occurs when i upload updated web pages to my site that already exsist.
For instance if i update some text or change an image on any given page and upload the new page under the same name.
When i do so the page won't immediatly show and on some occasions takes up to a week to change from the older version, this has since got a bit worse and now it decides to show me the old page sometimes on some computers, and the new on other occasions. It also differs accross the two variations of my domain name, i,e: and

Does anyone have any ideas why this occurs and what i can do to ensure the pages are availible quicker and more consistantly?

Thanks for all your time in advance.
Sounds like it's a caching issue. The files are being held in a memory cache until either the cache expires or the web process is bounced. I'm guessing your host uses an apache farm rather than dedicated server-per-site model. I see this problem at work all the time - the apache process has to be bounced in order to force a refresh of the cache. You *might* also be able to circumvent this by adding no-cache or cache-expiration headers to your html documents.

Contact your host and see if they can help you ferret out the best solution for you.