If you have problems uploading files to your server, or if you have a problem with larger files, you may need to make som adjustments to the php.ini configuration.
Some hosts allow you to upload a php.ini file to your root folder. This is the prefered way to make the adjustments. If you can't use a local php.ini you can make the same changes in a apache .htaccess file.
Here you will find some info on the php.ini file.