How to set the value for Radio Buttons When edit?

When you populate your fields, you can check for the value:

<input type="radio" name="sex" value="Male" <?php echo ($sex=='Male')?'checked':'' ?>size="17">Male
<input type="radio" name="sex" value="Female" <?php echo ($sex=='Female')?'checked':'' ?> size="17">Female

Assuming that the value you return from your database is in the variable $sex

The checked property will preselect the value that match

This is easier to read for me:

<input type="radio" name="rWF" id="rWF" value=1  <?php if ($WF == '1') {echo ' checked ';} ?> />Water Fall</label>
<input type="radio" name="rWF" id="rWF" value=0 <?php if ($WF == '0') {echo ' checked ';} ?> />nope</label>

just add 'checked="checked"' in the correct radio button that you would like it to be default on. As example you could use php quick if notation to add that in:

<input type="radio" name="sex" value="Male" size="17" <?php echo($isMale?'checked="checked"':''); ?>>Male
<input type="radio" name="sex" value="Female" size="17" <?php echo($isFemale?'checked="checked"':''); ?>>Female

in this example $isMale & $isFemale is boolean values that you assign based on the value from your database.