Are you ‘ondemand’ or ‘onpremise’? if on demand, you can’t change this, but if on premise and you are running the latest version (1.16), review your account settings from the admin console login. You will see the ‘max’ attachment size as per your license there. This should be higher than 2Mb and then allow you to set the max size in your file attachment object accordingly. If you are not able to do this and are on version 1.16, please contact us via the support ticket where supporting screen shots can help us see what you are seeing.
If you plan to allow more than 4mb file attachments though, review this forum post in respect of default .net setting
as to where the files are stored, they are stored within the form data. there is no separate specific path. For the next release version 1.17, you will also be able to use the API if you want to handle the file attachments differently. PutAsset method is already available, but GetAsset will be available then as well