What will happen if I already installed vsftpd package? Shall I remove it and install the new one? 

Will this command install pureftpd or vsftpd? yum install ajenti-v-ftp-vsftpd
I see that pureftpd is now available on twitter? How to get that?

True, forgot to mention, iptables restart :)

Port blocked by firewall?

iptables -A INPUT -p tcp --dport 8000 -j ACCEPT

Should be:

Cannot access Ajenti after successful install? 
Your firewall could be blocking port 8000. Please follow the following steps to fix it. 
- Please login to your server with SSH. 
- Edit iptables (firewall) config file by typing the following command: vi /etc/sysconfig/iptables
- Before the line with "COMMIT", enter the following line:

iptables -A INPUT -p tcp --dport 8000 -j ACCEPT

- Ajenti should now be accessible on http://you-server-ip:8000