The only way to 'over plant' is to have so many there is no room for the fish to swim around, or reach the surface for air.
However, it looks like you have an Amazon Sword (or similar Echinodorus species) which will overgrow that tank all by itself. They get pretty large. If that's what the one in front of the rock is anyways, hard to tell in the picture.
With stem plants, you just pull up the plant, cut the stem, and replant the top. That's all there is to it. It will grow new roots at the lowest 'node'. You can just cut the tops off, which will make the plants 'bushy' if you want, where you cut the stem the top node will send off two shoots. You may not want that in a small tank though, so just cut the bottom section off and replant the tops.