Hello @Radajoly
Welcome to the EE community
Providing you have genuinely upgraded, and not taken out a new connection, then you will retain your number as a matter of course.
EE often supply a replacement SIM with upgrade phones incase there's a problem with your current SIM or won't fit your new phone.
If your existing SIM fits your new phone and is working, then simply swapping it absolutely is the best thing to do.
