Section 8 Can I ammend the notice period

I served a section 8 notice on my tenant in July for rent arrears on grounds 8, 10 & 11. The arrears were £4668 which equates to just over 3 months rent. They have not paid anything since receiving the notice and the arrears will have increased to £7483.40 (6 months rent) by the end of this week when the next payment is due At the time of serving the notice I had to give them 4 months notice. As the waiting time has reduced recently can I re-issue the notice under current notice periods? Anybody else had this experience? Kind regards Denboy