Drat, you've named your character Johnathan and just now realized that Johnny would've been better. We get it.
On Windows just use CTRL+F and on Mac CMD+F to open the Find/Replace toolbar. Or hit the icon.
The Arrows can cycle forward and backwards through instances of the word you searched
Replace will replace the word you find with the text you put in the Replace field. Leave the Replace field empty to simply delete the found text.
Use Replace All to replace or remove ALL instances of the found word.