First, Save Project File AS. Do this routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, the AS choice is available by clicking the caret to the right of the Save Project button on the toolbar. That way you're protected, and shouldn't lose anything.
Select (highlight) the clip on the timeline by right-clicking it. Click Replace Clip File. Windows Explorer appears. Double-click the new file.
If this leaves a gap, right-click in the gap and Close Gap. If this doesn't work for you, delete the clip on the timeline.
Position the red cursor at the split point where the new clip is to be inserted. Use the 'edge' buttons for accuracy... 
After importing the new clip to the bin (top-left), right-click it and Place on Sequence at Cursor.