RiemannSimplify[expr,level,cr,g]

simplifies the Riemann tensors of metric g using relations up to the given level (see usage message for InvSimplify). With cr=True contracted Riemann tensors are replaced by Ricci tensors. If g is a list of metrics then the command is folded over the list.

RiemannSimplify[expr]

uses the defaults $InvSimplifyLevel, $CurvatureRelations and $Metrics, respectively. See usage messages for those global variables.