drop layer/band from SpatialGridDataFrame

I have a SpatialGridDataFrame with 325 variables in the @ data slot. I want to drop the first layer. Seems simple enough. Any help? Thanks, Andy

str(monthly.sp)

Formal class 'SpatialGridDataFrame' [package "sp"] with 6 slots
  ..@ data       :'data.frame':	8060 obs. of  325 variables:
  .. ..$ values: num [1:8060] 127.5 31.9 127.5 127.5 231.1 ...
  .. ..$ values: num [1:8060] 127.5 31.9 127.5 127.5 231.1 ...
  .. and so on