Recalculate slider lengths is a command under the Timing tab in the beatmap editor. Usage of this is suggested after a BPM change is made if the beatmap already has sliders. 5f1h2g
This command will automatically adjust the length of every slider in the beatmap to the new BPM. Although most creators recommended checking every slider and adjusting its length manually, due to this tool's inaccurate and systematic nature.