In the XFormsManager web application, there is a file called properties.xml You should edit the file with new values for max upload
<property as="xs:integer" processor-name="oxf:request" name="max-upload-size" value="100000000"/> <property as="xs:integer" processor-name="oxf:request" name="max-upload-memory-size" value="10240"/>
Also, in the file act.xpl, you should change the value of the label
<xforms:label>file < 1Mb</xforms:label>
The Orbeon Manual has a more extended documentation on Uploaded File
