Reduce table space in oracle

hi all,

our Manager asked me to a procedure for reduce the table space. kindly help me for below issue.

PSAPSID size 2.5TB- 400 GB free(aftre table space reorganization)

means 2.1TB data fulled,

Our problem is a lot of disk size when we run full database backup .

we want only 100 GB free space, and we needs to delete remaining 300GB from oracle to filesystem .

kindly help me

Thanks

Karthik