I recently wanted to upgrade my Framed MN 2.0 bike to get a better climbing gear. It originally came with a 2X9, Front 28/38t Rear 11-34. My poor old knees just needed some help on the climbs.
Anyway here is a quick way to upgrade a fat bike which has a square taper bottom bracket.
Go find a square taper crankset to use. I got the GANOPPER Square Taper Crankset with 32T Narrow Wide Chainring
Find a cassette that has a larger climbing gear. I went with microSHIFT Advent Cassette
Get the tools you need Crank Puller Loctite for the screws.
Optional but recommended. Replace the bottom bracket while you have everything off and check your chain if it is stretched out. I went with this one which fit my 100mm frame.VGEBY1 BB and I got a bottom bracket removal tool
You can find tons of videos on pulling cranks and installing square taper bottom brackets. So search it up and make that old bike a dream to ride.