Advice Needed please: Virgin /Delta code share flight

Hi all V-Flyers,
I wondered if you can shed some light on an upcoming flight that I booked with Delta ?
Heading to Las Vegas on VS43 / 44 Economy outbound (X) and Premium(G both Delta codes ) return, compared both Delta & Virgin and Delta were coming up £230 less than VA so booked with Delta.
Been checking the VA site and a G is available on the return leg so I phoned VA to ask how do I go about upgrading using miles or money or both but was told to contact Delta.
I phoned Delta and they said contact Virgin, explained that I had but was told theres nothing they could do unfortunately.
My instinct tells me no upgrade with miles as I booked with Delta but not sure about the money side upgrade ?
Hope I haven't rambled too much but any advice is appreciated.
I wondered if you can shed some light on an upcoming flight that I booked with Delta ?
Heading to Las Vegas on VS43 / 44 Economy outbound (X) and Premium(G both Delta codes ) return, compared both Delta & Virgin and Delta were coming up £230 less than VA so booked with Delta.
Been checking the VA site and a G is available on the return leg so I phoned VA to ask how do I go about upgrading using miles or money or both but was told to contact Delta.
I phoned Delta and they said contact Virgin, explained that I had but was told theres nothing they could do unfortunately.
My instinct tells me no upgrade with miles as I booked with Delta but not sure about the money side upgrade ?
Hope I haven't rambled too much but any advice is appreciated.