there is no universal way for this, but some general pieces of advice may help:
if you need to remove the something in template, you should remember that all templates are in “design/themes/THEME/templates” directory so you should search there.
the next thing is that you should use content search in TPL files (in subdirectories of directory from point #1), usually by unique CSS class or sometimes by language variables:
2.1. In your example it is a good idea to search by [color=#282828][font=arial, verdana, tahoma, sans-serif]class=“customer_notes” [/font][/color][color=#282828][font=arial, verdana, tahoma, sans-serif]or customer_notes[/font][/color]
[color=#282828][font=arial, verdana, tahoma, sans-serif]2.2 Go to admin panel in menu Administration → Languages, find text “[/font][/color][color=#282828][font=arial, verdana, tahoma, sans-serif]You can leave us a comment here” and get language variable ID to make content search in TPL files.[/font][/color]
p.s. After changes in template are done, don't forget to clean up the template cache to see effect.