Can a warlock willingly limit the use of its magic power? [closed]

A warlock’s pact magic spell slot levels power up by character level in DnD 5e.

Must I burn the whole warehouse by using Burning Hands or can I limit range and power? Essential question if wood and straw are surrounding me.

Some cantrips power up by character level too. But when I want to weaken a target and spare it for later interrogation, can I limit my use of cantrips or warlock spell slot power to a lower degree, or decide to use only one of up to four eldritch blast beams? Any official rules for this?

P.S: I don’t wanted to kill the kobold, I just struggled…with the dagger in my hand!