Rename the Add document link of a document library in sharepoint 2010

By using javascript function getelementbyid("idHomePageNewItem") we can change its display text to new text as we want

Open the document library in sharepoint designer. Open Alldocuments.aspx view in advanced mode.

Add the below script at the end of webpart zone
<script type ="text/javascript">
  document.getElementById("idHomePageNewItem-WPQ2").innerHTML="Enter your new text here"
</script>