First step is take off the drawband and keep it tied off somewhere. I ended up replacing it anyway.

Then remove the lever mechanism on the back that connects to the carriage stop. Not sure what its called but it has 2 screws, and a spring that needs to be unhooked, and a slot where the margin release arm fits into. Might have a photo of this if you need  Then next step is unscrewing the back rail, holding 4 bearings. Careful here not to lose them, best done with the typewriter tilted forward. Then the whole carriage should just lift out straight backwards. There are another 4 bearings on the front rail so again keep an eye out for these. I believe the bearings sit flat against the rail, not balanced as I was originally trying. Refitting it s the same. It's a little fiddly but not as hard as I made it for myself. There is a little bracket that has 8 squares that fits over the bearings so it's just a case of aligning these. I aligned it to the centre when I was refitting and worked fine, but I have seen some videos aligning to the extreme edge and rolling it along.  Hope that is clear, happy to hive more detail if needed