If I type a long paragraph which was intended to be written totally in small letters and later if i find that i have written it in Capital letters by keeping caps lock on by mistake,then is there any shortcut or process to convert that paragraph into small without typing it again?
It depends on where are you typing it? Most text editors allows selected text to be converted to upper case or lower case.
If your are using MS word, then you can do it like this: How do I convert lower case text to uppercase text in Microsoft Word?
There are no shortcuts for that built into any operating systems by default (Windows, Mac, or even Linux), but there are plenty of online utilities (and probably downloadable ones too) that you can use very easily. Here is one: http://convertcase.net/ and you can find a bunch more if you google capital to lowercase converter.
An interesting sidenote: many programming languages have methods like
toUpper() etc, that makes these tools really easy to create.