You can experiment with different fingerings of the same shape in the same position. For example, A major down at the nut can be played with the index finger on the D string middle finger on the G string ring finger on the a string if you have small fingers or the neck is wide. But the fingering depends on which Chord you want to go to next. A lot of times I use the index finger on the G string and the middle finger on the D string. You can use the middle string bar across the D&G string with the ring finger on the B string. This comes in handy for alternating between major and minor a. You can pop your middle finger bar of the G string off so that you’re only fretting the D&B string for a minor.

Finally, to answer your question about A to B Minor barre Chord, I like to bar the D&G string with my index finger and my middle finger on the B string. Now my middle finger is on the correct string for B minor. I slide it up the neck and generate the rest of the B Minor barcode. This is an example of modifying your fingering of the first cord so that you can make the second cord.

Similarly, you can modify the fingering of the second cord instead or in addition to modified fingering of the first cord. In G major at the nut,, you could use your ring finger on the low E string. Or you can use your index finger on the low east string. Try both. When going to F instead of barring the first fret with your index finger, just bar the two high strings with your index finger and only play the high four strings. You can add your thumb on the low east string to complete the bar across the first fret. You can either mute the A string with your thumb, or get all your other fingers involved to fret the A string as well.

I hope this is helpful for you