resizing LVM partitions

[Dave Burns]

lvresize preparation - how 'ensure filesystem shrunk'?
>From the man page:
   lvresize - resize a logical volume

SYNOPSIS[bla bla]

DESCRIPTION
       lvresize allows you to resize a logical volume.  Be careful when reduc-
       ing a logical volume's size,  because  data  in  the  reduced  part  is
       lost!!!   You should therefore ensure that any filesystem on the volume
       is shrunk first so that the extents that are to be removed are  not  in
       use.

so how do I do that? resize2fs