Ordered a new phone with O2, had a monthly rolling contract prior, how do I keep number?

[YordankaB]

I just received a new phone with O2 and a new 2 year contract, after previously having had a monthly rolling contract with them. I said at the time of ordering that I wanted to keep my old number, but received a new sim with the phone. Do I install the new sim and transfer the number, or will simply transferring my old sim to the new phone be enough? 
Side note - I'm not sure if the old sim is 5g compatible - does this affect anything?

[Bambino · Accepted solution]

@YordankaB You can use your old sim, which is more than likely only 4G, or you can do a sim swap to the new sim, if you're in a 5G area or will be frequenting 5G areas: SIM Swap: a mini guide (incl eSim) - O2 Community

If you aren't comfortable doing the sim swap yourself, call into an O2 store, if you have one nearby, and they'll do the swap for you. Be sure to bring identification with you.

[YordankaB]

Thank you!