There are two ways to get around this.
The permanent solution is to change php's upload_max_filesize variable.
In concrete5, the easiest way to do this is to add the following to your config/site.php
This will allow you to upload files up to 200MB in size. This option should work for most websites. Otherwise you will need to change the setting in php.ini. link
Depending on your hosting environment, that may not work either. Still another option is to modify your .htaccess file in your web root (usually public_html). Here is a discussion of the problem.
If you're just doing one file, or you do not want to make this change permanent:
- FTP the file into the files/incoming/ folder
- In c5's File Manager, choose "Upload Multiple"
- Pick the "Add Incoming" tab and select your file