to update the program can i use a old avast 4 version?
or need i to update the program a det version?
I sort of don't understand the question - what does it mean "to update the program"? I mean, if you have an old version (e.g. 4.0), you can update it just as usually - by invoking a program update - it will update to the latest build of avast! 4.5. If you have the latest version, there's no need to update, is it?
If you are asking about virus database updates, they can be done with the old version of the program as well (i.e. you can have the old program version and new version of the virus database).