How to change a dataframe column to lower case

[zhujp98]

# Import pandas library 
import pandas as pd 
  
# initialize list of lists 
data = [['tom', 10], ['nick', 15], ['juli', 14]] 
  
# Create the pandas DataFrame 
df = pd.DataFrame(data, columns = ['Name', 'AGE']) 

I want to change on of the field AGE to age, keep Name unchanged .
How Can I do it?
Thanks,
Jeff