subset problem (reducing from six to two levels)

Hi all,
I have got a seemingly simple problem (I am an R starter) with subsetting my
data set, but cannot figure out the solution: I want to subset a data set
from six to two levels, so that all analyses are done only with these two
remaining levels.
I tried

TOTAL<-read.delim('total.csv',header=T)
SUBSET.OF.TOTAL<-subset(TOTAL, FactorX %in% c("Level1","Level2"))
attach(SUBSET.OF.TOTAL)

but R does not eliminate the remaining levels of FactorX, just assigns 'not
available' to the data. Like this, the other levels still show up in plots
etc., but without data entries. Anybody got a solution how to subset the
data so that I eliminate the other levels completely?

Thanks a lot for the help,

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