How to rename related list in Salesforce standard relationship?

1. From Setup, go to Customize > Tab Names and Labels > Rename Tabs and Labels.

2. Click the "Edit" link next to the name of the child object.

3. Rename the Singular and Plural labels.

Note: Plural label is used to title related lists

4. Remember to "Save" when finished.

Check the below link for renaming tabs and labels.