Suppose if I have Future Stock of SEPTEMBER, but I dont want to sell it on 25th SEPTEMBER, rather than hold the stock to OCTOBER series, can I hold the stock or I must have to surrender the SEPTEMBER future stock on 25th SEPTEMBER.
All Futures expire on expiry day. If you hold September Expiry Futures it will automatically expire on 25th Sep, You cannot hold it further. This is what I know.
You can do what is called a rollover. Explained here