How to use LetsEncrypt on FTP connection?

Hello,
I have buy LetsEncrypt 2.0.5 and I have enable Control Panel and Service at System Tools tab.
My Control Panel and POP3/SMTP has use LetsEncrypt generate key.

Only FTP connection use old key.I has install startcom key in FTP before install LetsEncrypt key.

How to replace old FTP key?

I has test connection site use "panel.domain name" and "web1.domain name".It's will show key information.But it's always show startcom key.

My POP3 and SMTP has change to LetsEncrypt cert.But only vsftp use old cert.How to fix it?

Hello,I re-run "perl imscp-autoinstall -d",It's use lets cert now.

Debian 7

1.3.16