Is there any way to change the keys (not Values) in the dictionary in Python?

You can pop the value of the old key and reassign:

d = {'A': 1, 'B': 2, 'C': 3}
d['b'] = d.pop('B')

print(d)
# {'A': 1, 'C': 3, 'b': 2}

Note that this won't maintain the order of the keys (python 3.6+). The renamed key will be instead at the end.

maintaining order

If order is important you need to create a new dictionary

d = {'A': 1, 'B': 2, 'C': 3}

rename = {'B': 'b', 'A': 'a'}

d = {rename.get(k, k): v for k,v in d.items()}

print(d)
# {'a': 1, 'b': 2, 'C': 3}

in place modification while maintaining order

If you want to modify the dictionary in place (i.e. not creating a new object), you need to pop and reinsert all keys in order:

d = {'A': 1, 'B': 2, 'C': 3}
rename = {'B': 'b', 'A': 'a'}

keys = list(d)

for k in keys:
    d[rename.get(k, k)] = d.pop(k)

print(d)
{'a': 1, 'b': 2, 'C': 3}