If you have your own server, you can change the values for post_max_size and upload_max_filesize in the php.ini file. You will usually find this file in /apache/bin.
If you are using someone else's server (such as a hosting service), you probably can't change anything in php.ini. Try creating a file called .htaccess in the root of your Moodle installation that contains the following lines:
php_valuevaluepost_max_sizesize128M php_valuevalueupload_max_filesizefilesize128M
Replace 128M with any value that you need. If the server times out while uploading large files, you might add lines like the following to .htaccess:
php_valuevaluemax_input_time 600 php_valuevaluemax_execution_time 600
The ...
