Hi Syvia,
As
alizaied01 says, you can change the default name of a user corpus when it is first created in the interface. But, changing the name *after* the corpus is built is more difficult. At the moment, there is no way to do this within the interface, but you can open the corpus database in any SQLite database viewer and edit the name directly. All the information about the corpus is held in the "corpus_info" table.
This is certainly a feature I intend to add to AntConc 4 in an upcoming release.
I hope that helps!
Laurence.