Help > Authoring > Equations > Editing Equations > Replacing Symbols and Constructs
  
Replacing Symbols and Constructs
1. To replace a single symbol or construct with another, move the marker over it and choose Commands > Replace This Object.
The region, occupied by the symbol or construct, takes on a dotted appearance to signify replace mode.
2. Choose the replacement from the Symbols or Constructs menus.