Hi Prabhaker,
Thanks for your inquiry. All text of the document is stored in runs of text. In your case, I suggest you Run.Text property to get or set the text. You may also use following code example to remove run nodes of Paragraph and add new Run node into Paragraph.
Moreover, I suggest you please read about Aspose.Words document object model from here:
https://docs.aspose.com/words/java/aspose-words-document-object-model/
Document doc = new Document(MyDir + "in.docx");
Paragraph paragraph = (Paragraph)doc.getChild(NodeType.PARAGRAPH, 0, true);
paragraph.getRuns().clear();
Run run = new Run(doc, "modified text");
paragraph.appendChild(run);
doc.save(MyDir + "Out.docx");