In the early stages of the software development process, formal methods are used to engineer specications in an explorative way. Changes to specifications and verification proofs are a core part of this activity, and tool support for the evolutionary aspect of formal software development is indispensable. We describe an approach to support evolution of formal developments by explicitly transforming specifications and proofs, using a set of predefined basic transformations. They implement small and controlled changes both to specifications and to proofs by adjusting them in a predictable way. Complex changes to a specification are achieved by applying several basic transformations in sequence. The result is a transformed specification and proofs, where necessary revisions of a proof are represented by new open goals.