Aristotle's Poetics is the oldest extant text that defines the term peripateia. In William Hamilton Fyfe's translation (1926; [1452a]; emphasis mine):
Some plots are "simple" and some "complex," as indeed the actions represented by the plots are obviously such. By a simple action I mean one that is single and continuous in the sense of our definition above, wherein the change of fortune occurs without "reversal" or "discovery"; by a complex action I mean one wherein the change coincides with a "discovery" or "reversal" or both. (...)
A "reversal" is a change of the situation into the opposite, as described above, this change being, moreover, as we are saying, probable or inevitable— like the man in the Oedipus who came to cheer Oedipus and rid him of his anxiety about his mother by revealing his parentage and changed the whole situation. In the Lynceus, too, there is the man led off to execution and Danaus following to kill him, and the result of what had already happened was that the latter was killed and the former escaped.
The example from Oedipus is a reversal in a negative direction. The Lynceus is a play by Theodectes based on a mythical story about Lynceus of Argos. The play has been lost, but it appears that Lynceus escaped death, so the reversal in Theodectes's play is a positive reversal for the main character.
J. A. Cuddon's The Penguin Dictionary of Literary Terms and Literary Theory (third edition, Penguin, 1991) writes that a peripateia in drama is "usually the sudden change of fortune from prosperity to ruin; but it can be the other way about". The entry for "peripateia" also cites an excerpt from Aristotle's Poetics (from chapter 11 in Ingram Bywater's translation) but without including the Lynceus example.
Some reference works for literary terms consider peripateia as an exclusively negative change, for example LiteraryTerms.net, but others also provide examples of positive changes, for example, LiteraryDevices.net. The Algemeen letterkundig lexicon (in Dutch) says that a peripateia can be either a positive or a negative reversal.