Dear Raja,
we had a similar problem with one of our tables. If I remember right, it is not possible to re-use the old segment by deleting some rows.
So we created totaly new dbspaces for the different fragments and altered the table, e.g.
alter fragment on table xxx init
fragment by expression
(column1= "expression1") in dbspace1,
(column1= "expression2") in dbspace2,
...
remainder in dbspace8;
In our case we used expression based fragments, also possible is the round-robin-fragment. What makes sense depends on your data.
I'm not sure if this is the best solution, but it worked fine.
Good Luck
Regina