When you right-click the row header you get a menu that gives you some options :
** Delete Selected Rows
** Delete Row Contents
Each command does as it says .
Same thing with the columns .
Addition to my answer
After reading your comments :
1) Check this image .
Is that what you are looking for ?

2) To do this , you have to select the rows and hide them ,
and then select the columns and hide them .
3) Selecting rows 9 till end of file is done like karolus wrote :
selecting header of row 9 , then pressing shift+ctrl+end+arrow down .
4) In selecting columns , you press shift+ctrl+end+arrow left .
5) All the information in the hidden cells still exists there ,
and you don't get smaller size files just because you don't exhibit some cells .
6) What possessed you to think that someone didn't bother to read your question
before answering it ?
My English is as bad as your English !