best way to replace content within span id

Hi folks. I'm looking for the best way to replace the content within the following:
<span id="QueryScreenControl1_lblPageHeader" class="query_tblheader" style="width:712px;">Some Name: Catalog</span>
so that what displays is only:  Catalog
I've executed the attached code, but need something that will work more broadly. For instance, let's say I've got the following: <span id="QueryScreenControl1_lblPageHeader" class="query_tblheader" style="width:712px;">Some Name: Serials</span>
then I want to end up displaying only:  Serials.
Or suppose I have the following: <span id="QueryScreenControl1_lblPageHeader" class="query_tblheader" style="width:712px;">Some Name: Something Else</span>
then I want to end up with:  Something Else
Perhaps I should use innerHTML.replace and a RegEx? Please advise. Am looking for a good solution that doesn't require multiple "ifs" and "thens"
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if(document.getElementById("QueryScreenControl1_lblPageHeader") !=null) {
   if(document.getElementById("QueryScreenControl1_lblPageHeader").innerHTML=="Some Name: Catalog") {
      document.getElementById("QueryScreenControl1_lblPageHeader").innerHTML = "Catalog"
      }
}