How to destroy ( Kill ) a particular ( specific ) Session in ASP.Net

Que. I want to set timeout of particular session.for e.g. in web.config session timeout is set to 30.

when user enter in particular page say test.aspx we create new session say session("a")=3.

after that user enter to new page say xyz.aspx .

CASE 1:

i want to  set timeout of session("a") to 10.

CASE 2 :

i want to distroy this particular session (i.e session("a")) not all the sessions.

CASE 3 :

i dont want user can use session("a") on this page but other session's should be accessible.