How would this work

Hi all,
Firstly, thank you so much for all your help in recent times, hopefully you might be able to answer this one. Here are the plans so far:
Outbound - Sept 16 2 adults 1 infant UC LGW-MCO
Inbound - Sept 16 2 adults 1 infant PE MCO-LGW
The Inbound flight was using the upgrade Econ-Prem Econ with the black card. Paid using miles. I didn't have enough miles then to cash in and get UC.
If my some miracle, I noticed now that 2 spaced showed up in UC on the way home is there a way I could 'cancel' my inbound PE seats and get the UC seats? If so, approx how much would this cost me, and would I get my miles back?
Any chance of getting these seats with only 4 months to go?
Firstly, thank you so much for all your help in recent times, hopefully you might be able to answer this one. Here are the plans so far:
Outbound - Sept 16 2 adults 1 infant UC LGW-MCO
Inbound - Sept 16 2 adults 1 infant PE MCO-LGW
The Inbound flight was using the upgrade Econ-Prem Econ with the black card. Paid using miles. I didn't have enough miles then to cash in and get UC.
If my some miracle, I noticed now that 2 spaced showed up in UC on the way home is there a way I could 'cancel' my inbound PE seats and get the UC seats? If so, approx how much would this cost me, and would I get my miles back?
Any chance of getting these seats with only 4 months to go?