Look around in the API documentation of the classes String and Character.
If you have a string and you want to remove all the digits from it, you could write a loop to go over all the characters in the string. You can use Character.isDigit(...) to see if a character is a digit or not. In the loop, append the characters to a StringBuilder (or StringBuffer) and skip over the characters that are digits.
Please try to write this code yourself - and if you have difficulties, show us what you wrote and tell us why it doesn't yet work as you want it.