How to change the owner of a file in Linux
You need to use the chown command:
1. To change the owner of text.txt to john
# chown john /tmp/text.txt
2. To change the owner of text.txt to john, but group identifier to admin.
# chown john:admin /tmp/text.txt
3. To change the group of text.txt to admin
# chown :admin /tmp/text.txt