Once you turn the text into a path, you can't do any more kerning. The letters, in essence, turns into objects, not letters. If the letters are grouped, you can ungroup them and move each letter individually. If they're not grouped, the words might be one object. So instead, you'll have to break them apart (Path>Break Apart). This will make each shape and will make your letters look like big blobs. Select all the components that make up that letter and combine them (Path>Combine) to make it look like a regular letter. Now each letter is separate and can move them individually.