Nearly always caching - something between you and the file is serving an older copy.
Check in this order
- Your browser. Open the site in a private window. If the change is there, it was your own cache.
- A caching plugin. Clear its cache from the site's admin.
- A CDN. If the site sits behind one, purge it too.
- Server-side caching. Ask us to clear it if the above has not done it.
Make sure the change actually saved
Reload the editor and confirm the new content is there. Check you edited the page you think you did - duplicate pages and drafts catch everyone out. If you uploaded a file, confirm the timestamp changed.
Are you looking at the right site?
If you have a staging copy, make sure you did not edit that. And if you recently changed DNS, you may be seeing the old server - see What DNS propagation really means.
CSS and images specifically
Stylesheets and images are cached hardest. A hard reload usually shows the truth. If the file is right on the server but wrong in the browser, it is cached.
Still not showing
Tell us the page, what you changed, when, and whether it appears in a private window. That distinction alone tells us where to look.
