How do I set up a new SIM on the same phone

[YouReallyAre]

I have ordered a new SIM card as I have got a better deal with a new provider. Do I request the PAC from my current provider first and then once I've received that, take that SIM card out of my phone and put the new one in?

I have googled but everything assumes you have a new phone alongside your old one whereas I don't so I am a bit confused. Thank you!

Request PAC, give it to your new provider, number will usually transfer the next working day if you give it to them before 5pm. Put new SIM in phone and it will start working at some point the next day - useful if you have an old phone to put the old sim in so you have at least one of the working most of the time.

@IsThisNameTaken thank you. Unfortunately I don't have an old phone so will have to wait until Monday before I do the transfer so I'm not without my phone all weekend.