if you mean the about me bubble it is an image located in this directory:
A manual way of doing it would be to replace that image with one containing the text you want (i.e. make a speech bubble image in photoshop and replace the original)
This, however, does not seem the easiest way to do this and the only other thing I could suggest is in wp-admin, the theme you are using should have its own control panel (under “themes” > “theme settings”) where theme is the name of your theme.
There I would hope there is a box to edit the text that appears in that bubble image although I am not familiar with that theme