Again, the anchor point tool is necessary here. First you drag the top line up to add split anchors (or cusp nodes, haven't ever used that term) to the two adjacent points. Then you can use either the anchor point tool or the direct selection tool to adjust the two new anchors.
One feature Adobe Illustrator is sorely lacking (afaik) is grid snapping for anchors. They will snap to objects, lines, and points, but grid snapping would be really helpful.
Again, the anchor point tool is necessary here. First you drag the top line up to add split anchors (or cusp nodes, haven't ever used that term) to the two adjacent points. Then you can use either the anchor point tool or the direct selection tool to adjust the two new anchors.
The anchor point tool is essential to using Illustrator. You can read more about it under "Convert an anchor point precisely using the Convert Anchor Point tool" here: https://helpx.adobe.com/illustrator/using/editing-paths.html
One feature Adobe Illustrator is sorely lacking (afaik) is grid snapping for anchors. They will snap to objects, lines, and points, but grid snapping would be really helpful.