Depends on what type of button you are using
<input type='button' value='Add' id='btnAddProfile'>
$("#btnAddProfile").attr('value', 'Save'); //versions older than 1.6
<input type='button' value='Add' id='btnAddProfile'>
$("#btnAddProfile").prop('value', 'Save'); //versions newer than 1.6
<!-- Different button types-->
<button id='btnAddProfile' type='button'>Add</button>
$("#btnAddProfile").html('Save');
Your button could also be a link. You'll need to post some HTML for a more specific answer.
EDIT : These will work assuming you've wrapped it in a .click()
call, of course
EDIT 2 : Newer jQuery versions (from > 1.6) use .prop
rather than .attr
EDIT 3 : If you're using jQuery UI, you need to use DaveUK's method (below) of adjusting the text property
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…