how do I update the files in /boot folder?

Solution 1:

The answer for most users:

• You don't touch those files. You do not update them. Leave them alone. Apt will automatically update them for you...when updates are available.

• That directory should properly have a set of files for each installed kernel. There should be two or three sets of files (two or three installed kernels). There may be differences between the sets: If one file is missing or extra, but your system boots properly, then DON'T try to "fix" or "repair" it -- it's not broken.

• Some of those files are essential for your boot. Do not try to "improve" or "update" or "clean" them or otherwise "help". Doing so incorrectly may result in an unbootable system. Leave them alone.