The replace command is related to the search command in that a string is searched for and, when found, replaced. Invoke replace from the EDITING menu or with Alt-r. Point first asks you for the string to be searched for, and then for the string with which it is to be replaced. Next, you are asked whether to do the replace from the selection to the end of the file (globally), or only within the selection. Finally, you are asked whether you want to verify each replacement. If you answer 'y' (yes), you will be asked each time the string is found whether you want it replaced or not.
The replace search is affected by ignoreCase and searchMode in the same was search is.