Deselect current category while bulk moving of posts

Hi..
This is my first post in wp forum though i keep visiting often and i appreciate the help and support here and the open community.

I have moved a category, say ‘A’, from under parent category, say ‘X’, to under a new parent category, say ‘Y’.
from:
-X
–A
to:
-Y
–A

I tried the following:
-> Go to ‘All Posts’ in admin panel.
-> Filter category A.
-> Select all posts.
-> Select ‘Edit’.
-> Select category Y.

My question is:
Now, categories A, X and Y all have the posts within!
Is there a way to deselect category X?

Note:
1. i cannot see any categories selected after going into ‘Edit’ mode.
2. i need to retain X because it has many other subcategories and posts.
3. not a fanboy of plugins. hope there is a better way. 🙁

Please do help me on this.
Thanks in advance.