Need to purge DB tables

Hi! Our DB has grown considerably. We are trying to purge the DB table
ACT_HI_ACTINST which is having a size of 181gb. Although, we already deleted info of the table (2 years aprox and which did not really do something to the size) and left only the past year of data, size is still quite large.
Is there anything that we missed? how can we make sure that we properly deleted the data?