I received this to my TM phone: "T-Mobile: Introducing the Free 5G upgrade...."

I got the same message. I'm on a 2GB plan. (Which century did you get the 30MB plan from?)

Anyhow, it looks like it's exactly what it says. T-Mobile is giving us a free 5G unlimited upgrade. You don't have to do anything, you just get 5G speeds with no limit, except for only 6GB of tethered data at 5G speeds. Of course we'll need a 5G device and live where there's 5G service to actually get 5G speeds. I only have 4G phones on all 4 lines. But it's a really nice bonus from T-Mobile! And at the same price ($100 for 4 lines for me). I'm not complaining!

If you change plans then you lose your current price and could lose the 5G unlimited service, depending on what plan you get and what T-Mobile is offering.