HOW TO
The JSON representation of a service in the ArcGIS Server admin directory has a parameter, "maxuploadfilesize", which can be modified to manage the upload size of attachments in a feature service.
By default, the value for maxuploadfilesize is in megabytes (MB) and is set to 2000. This value can be decreased to restrict the upload size for attachments or increased to accommodate more/larger attachments.
http://<server-name>:6080/arcgis/admin
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