If you mean the unneeded rests at the beginning of a pickup measure, then right click the measure, choose measure properties and adjust the actual duration of the measure. In version 3 you can select a rest and press ctrl+del. There was a bug that if some of the parts did not have individual rests of the same duration you want to delete this would cause a corruption, but I don't know if it's been fixed.
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If you mean the unneeded rests at the beginning of a pickup measure, then right click the measure, choose measure properties and adjust the actual duration of the measure. In version 3 you can select a rest and press ctrl+del. There was a bug that if some of the parts did not have individual rests of the same duration you want to delete this would cause a corruption, but I don't know if it's been fixed.