hey
Maintain or release the tension?

You have to be more specific. The decision is completely contextual. It pretty much depends on whether you will likely come out on the short end after the opponent releases the tension or if you will get some initiative from play after the exchanges.
Suppose I reach a position where I have solid pressure against the opponent's center pawns, but my opponent has everything adequately defended. How do I know when it's better to maintain the tension, and conversely when it's better to release the tension?