How to free Inode ?

Inode is full how to make it free

Recently I come across the situation where I am unable to create a empty file on server even though space is available on server. Then i checked the inode by below command

df -i

It showed that my inode is 100% full due to this i am unable to create anything on the server.

Then we did du -sh * for all directories. During running the command du -sh * some directory is taking too much time to give output. When we checked inside that directory it contained lot of empty files.When we cleared those files we checked the inode it is free now. WOW!