The maximum upload size can be adjusted for each resource type in its configuration, but sometimes you might want to upload a file and the process will fail. This is usually due to the maximum size allowed for an Asp request in the server configuration.
In order to fix it, if you don't have direct access to the server you should ask your hosting provider to increase this limit for you. If you have full control on the server, then you can follow the steps outlined in this MS KB article or follow this other visual guide.