My visa is due to expire 25th May, how long before that date should I track down to Immigration to renew it?? Closer to the date is better? Does it matter, do they extend it from the 25th anyway. What is the procedure. Help would be appreciated. This is a first one for me, sorry for the hassle, I just can't find the info here.

What do you mean by renew? You obtain visas from Consulates. From Immigration you obtain extensions of stay (normally for one year but for language students it may only be 90 days). All extensions of stay should be obtained during the last 30 days of current permitted to stay stamp. So 2 week before would be good at most places. The extension will start at the end of current permitted to stay stamp.

What kind of visa do you have?

You state that visa is due to expire 25th May.

What is the date on your arrival stamp?

In order for you to extend your Ed visa, you will need some documentation from the school you are attending, that comes from the Ministry of Education. Check with the school to get the information needed.