A user asked me why, when he attempted to upload an Access database in place of another one, he got errors indicating that the file is in use by another process. Access is a file-system database, which means that everything dealing with the database is in one file. The problem is that if someone is using a web page that uses the database, the web server locks the database file open. The only safe time you can replace it is if no one is using the database. This generally means stopping the web server long enough to replace the database.
Instead of this method, I prefer to create a user interface for updating/modifying/deleting data in the database, no matter which database I’m using. It prevents this problem completely with Access since if I’ve got a UI, I don’t need to fix the database directly. The exception would be a database structure change (new tables, queries, etc.). In this case, I stop the web server, make the changes, and then start the web server again. I try to avoid making structural changes on the fly, but on occasion, you have to do it.