Is there a way to change font size of a batch of text within a document

Question

I have a bunch of text that needs to change its font size. The text block I want is in the middle of a document.

So right now, what I do is below. I keep getting some bunches of text not changing font size. Is there a better way to do this? I tried going word by word but that takes visibly long time to complete. Also trying the find whole text via TxControlObj.Find method gets Out Of Memory Errors.

       // processedText is the block that needs to have the changed font size
       while (processedText != String.Empty)
        {
            if (processedText.Length > 50)
                processRange = 50;
            else
                processRange = processedText.Length;

            startPos = TxControlObj.Find(processedText.Substring(0, processRange), startPos, TXTextControl.FindOptions.NoMessageBox);
            TxControlObj.Selection.FontSize = fontSize;
            processedText = processedText.Remove(0, processRange);
        }
        //This last bit here is because, I get highlighted text at the end of the loop otherwise.
        startPos = TxControlObj.Find("", startPos, TXTextControl.FindOptions.NoMessageBox); 
        TxControl.Update();