From the server console:

mkdir -p /var/opt/xen/iso_import

xe sr-create name-label="MyISORepository" type=iso device-config:location=/var/opt/xen/iso_import/ device-config:legacy_mode=true content-type=iso

wget <something> -P /var/opt/xen/iso_import

From: https://discussions.citrix.com/topic/250684-import-iso-image-to-xenserver/