In this task, you need to replace a letter in the sentence with another given letter.

Example Input: Sentence: 'a person on a surfboard riding in ocean waves'. Replace the letter 's' with 'g' in the sentence.
Example Output: a pergon on a gurfboard riding in ocean waveg

Example Input: Sentence: 'some brown black and white horses clouds and rocks'. Replace the letter 'a' with 'n' in the sentence.
Example Output: some brown blnck nnd white horses clouds nnd rocks

Example Input: Sentence: 'when it's this cold, it's better to stay out of the wind'. Replace the letter 'h' with 'g' in the sentence.
Example Output:
wgen it's tgis cold, it's better to stay out of tge wind