Short answer: Don't. They are good as they are. It would be better to think about why you would use the passive voice. For example: i) You don't know who is doing the action, ii) The action is done to you/a subject and not by you/a subject, iii) We don't want to say who is doing the action.

"The car is owned by me." "To support a career, these are the eight skills that are needed by a top manager." These are quite ugly; there is a strong style preference in English for active sentences, by and large, and except where the passive voice is needed for clarity or emphasis. Sometimes, though, writers trying to seem serious and academic can lean more on the passive.