A lot of times developers do one or other mistakes and you need to revert the files to older version. Which basically mean that you need to merge backwards with a older version of files. So let’s say if you want to go back from version 100 to 99, you’ve to
svn merge -r 100:99 .
svn commit -m "Rolling back to version 99"
Notice the . at end of svn merge command, this tells that current directory needs to be merged if you need a particular file to be merged you need to issue
svn merge -r 100:99 conf.php
svn commit -m "Rolling back conf.php to version 99"
Hope this helps someone.