Need help in reclaiming disk space by deleting the selected records

Hi All,

I am a beginner in Postgresql and Databases. I have a requirement that reclaiming disk space by deleting the rows in a selected time span. I went through the documents and articles to know how to get the table size (http://wiki.postgresql.org/wiki/Disk_Usage)

But before let the user delete, I have to show the size of the records size in the selected time span. But here I don't know how to calculate the selected records size.
In addition to this, I assume that after deleted the records I have to run VACUUM FULL command to reclaiming the space( Please correct me if I am wrong or let me know the best approach) .

The table looks like this

CREATE TABLE IF NOT EXISTS "SN_SamplTable"
(
"ID" integer NOT NULL,
"Data" integer,
"CLIENT_COUNT_TIMESTAMP" timestamp without time zone
);

Please help me to how to proceed on this.

Thanks & Regards,
Ramkumar.