First login into your server using Putty.
Step 1:
# apt-get update && apt-get upgrade && apt-get dist-upgrade
Step 2:
# wget https://vestacp.com/pub/vst-install.sh
Step 3:
# bash vst-install.sh
or
# bash vst-install.sh --force
Then enter your email, host name and wait 15 mins.
After that you will see your login details.