After New Installation do te below

1. Copy Admin Templates file to WHMCS-v/admin/templates 
Template/Folder Name = accessystem_v6
and the below files also
accessystem-logo-long-email-temp.png
accessystem-logo-long.png
accessystem-logo-long.jpg

2. Copy Invoice Template from corrent setup to new Setup (  templates/six folder )
invoicepdf.tpl
viewinvoice.tpl

CSS File Also(  templates/six/css folder )
invoice.css

3. Company Logo Link in General Settings & General Settings/Mail
Company Logo Link
https://manage.i-host.in/admin/templates/accessystem-logo-long-email-temp.png

General Settings/Mail - Header
<img src="https://i-host.in/admin/templates/accessystem-logo-long-email-temp.png" style="max-width:300px;padding:30px;margin:20px" id="headerImage" alt="{$company_name}" />

4.  # Invoice PDF Logo Logo
Copy  accessystem-logo-long.png & accessystem-logo-long.jpg in /assets/img/
And chnage the below in invoicepdf.tpl (  templates/six folder )

$logoFilename = 'accessystem-logo-long.png';
if (file_exists(ROOTDIR . '/assets/img/accessystem-logo-long.png')) {
    $logoFilename = 'accessystem-logo-long.png';
} elseif (file_exists(ROOTDIR . '/assets/img/accessystem-logo-long.jpg')) {
    $logoFilename = 'accessystem-logo-long.jpg';
}
$pdf->Image(ROOTDIR . '/assets/img/' . $logoFilename, 15, 15, 70);


$pdf->SetFont($pdfFont, 'B', 20);



public_html/Web-Apps/WHMCS-7100/admin/templates

5.  Please check the file /admin/whatsnew.php to remove any un-wanted pop-up