How to add or remove an underline for links in Blogging Post

Login to your account. Go to Layout > Edit HTML.
Search for a:link (Tip: Use Ctrl + F)
You will see a similar code there as:

a:link {
color:$linkcolor;
text-decoration:none;
}
a:visited {
color:$visitedlinkcolor;
text-decoration:none;
}
a:hover {
color:$titlecolor;
text-decoration:underline;
}

The above code specifies that there is no underline as dictated by text-decoration:
text-decoration:none

Here none specifies "No Underline". To add underline simply change the command to:

text-decoration:underline

If it was originally underlined simply change it back to, yea you guessed it right ;)

text-decoration:none