Hello aspirant,

Since you haven't mentioned about the subjects you wish to find your e-book on, I will give you a general overview. There are certain websites which let you avail e-books of updated versions such as z-lib.org (//z-lib.org) . You however, will not find e-books of authors who don't make their exclusive edited versions available on the internet. Since these online versions aren't edited or uploaded quite often, you will sometimes get older versions of the same book. The  best solution in this case is to buy second hand books of the more recent versions.

Hope this helps.