How can you ever upgrade

I’m having a real frustrating time and would love if someone could advice. I’m not new to virgin or their flying club but I’m new to not being able to upgrade prem to uc with miles.
I have done the normal one way searches for rewards and found flights that work for me but they are all on delta and you can’t upgrade on delta so how do I search for flights I can use miles to upgrade on?

What route & dates are you after?

You can use VS miles to upgrade on Delta.

you can use VS miles on DL as long as you booked via VS

Call the flying club they are very helpful.

All good advice thus far, but lest we forget, award space in the cabin you wish to upgrade into (in this case Upper) needs to be available. You also need to have the right kind of fare bucket, which for Premium will be H, S or W. If you've booked a K fare (either knowingly or unknowingly) you will not be able to upgrade with miles, but you will still be eligible to upgrade at the airport on the day of departure for a fixed fee - subject to availability.

This is all very route and date dependant too. Some routes have lots of availability (JFK for example) and some have little to no availability (LAX) and it all depends on the number of seats available & load factors in the premium cabins. For example, you can pretty much wave goodbye to getting Upper Class reward seats on most of the Caribbean operated 747 routes due to few Upper seats and extremely good availability of fare paying passengers. Not impossible, but highly unlikely.

Anyway, good luck. Please let us know more info and let's see if we can help nonetheless.

Thank you for the replies I have called flying club twice yesterday can someone confirm that you can’t upgrade delta flights booked through virgin with virgin miles ( the route I was looking for was London to Nashville and flexible dates in September) I found a reward seat available via Boston on the website ( it’s still showing ) but the very grumpy flying club assistant said you can’t upgrade on delta but I tried to explain to him that I can see a reward seat available he said yes they are different you can use miles for a reward seat but not upgrade .... is that other people’s experience? ( byt I got reward seats in upper to cancun every year until they stopped flying )