Changing Module Headings in Class details pages

In the details pages of classes, I would like to change the following module headings. Please let me know which files to modify and where. Thanks.
1. Change “Class information” to “Session information”
2. Change “Class Trainer” to “Session By”
3. Change “Relate Class” to “Related Session”

Thanks for the prompt reply. However, I had tried that file before but did not find in it the text I should edit. For example, the file does not contain the term "information." Please give me more specific directions. Thanks a lot.