Many web hosts limit this to 2Mb. You can see your current server settings by logging into arpReach and going to Help / About / System.
You need to make sure your file is no larger than what is indicated as your 'Admin upload max file size'.
If you wish to increase your upload size limit, contact your web host to increase your limits for the following:
You also need to make sure that you have enough available memory to handle the upload as well, so you might need to ask them to increase it for you.