Aer Lingus Flight Change options

Hi,
Booked a week with the family in the Canaries in January.
It turns out now that I would need to change the return flight - simply to an earlier flight on the same day.

Wondering what my options are:
1. Change the flights
- seems really expensive to do this
2. Cancel and re-book
- Not sure what kind of refund I would get approx 5 weeks before flight date - anyone know?
3. Book new flights - probably Ryan air for at least 2 of the party
- what happens if only 2 of the 4 people in the original booking check-in?
4. Other options
- Any suggestions

Also the complication with this is that I booked through travelrepublic.ie - I have contacted them through their website but have not heard back yet.

Appreciate any guidance