Heraclitus was not only spare in his explanations, but his only known work exists merely in fragments. The piecemeal verses we still have of his writing render it difficult to tell if he was being unintentionally vague, or if he thought his statements were self-explanatory.
While his thoughts regarding "flow" are translated with varying degrees of difference, they usually share the same general sentiment, and complexity, as the "you can't step in the same river twice" adage. This is typically interpreted in both a literal and metaphorical manner. The river physically changes always. The very fact that this change is present, and yet often escapes our notice, brings attention to the fact that similar changes take place in everything. Therefore, everything is changing, or is capable of change.
A more nuanced view might analyze the concept in comparison to Plato's Theory of Forms. A carpenter, for example, might never be capable of creating the "perfect" chair; yet the idea of the perfect chair informs the carpenter's work. The perfect chair is an idea, and always will be; does the fact that it can never exist make it less "real" than the chair that actually exists before us?
In his meditation on change, Heraclitus might be seen as agreeing with Plato's premise of constant change and improvement. The "real" manifestation of an idea—the river—is always changing, both in the manner in which it manifests and in its composition. So while the physical manifestation is physically more "real" than an idea, we rely on the idea to describe and judge the object. That judgment may be inherently flawed if it fails to take into account the impossibility for the real object to surpass the very changes that separate it from the infallible idea and render it subject to judgment in the first place.
Heraclitus might go a step further and say the idea is also changing, just as we might not even agree on what name to call a river. This implies that even the things we might consider to be immutable facts are, in the long term, impermanent. Based on that theory, change is not problematic and should be included in how we evaluate the forms that our ideas take.