To replace a yarn (colour) or stitch type that is used by any stitch in the chart, delete the relevant entry from the key. As the entry is deleted from the key the user will be prompted to replace the yarn or stitch type with an alternative.
To replace a yarn or stitch type;-
Select its entry in the key (see Selection Tools).
On the main menu bar, select either Edit > Cut or Edit > Delete. Either the Replace Stitch Type dialog or the Replace Yarn dialog opens.
Select an alternative yarn / stitch type.
Alternatively use the keystrokes Control+X (on Windows) or Cmd+X (on macOS) or select the Cut / Delete Icons from the toolbar.
Alternative sources of explanation: