1-Click Upgrade prestashop version issue

[thedestiny]

hello, i have try to update latest version on prestashop using 1-Click Upgrade

when i click upgrade prestashop now and show ajax response

siteurl + admin/autoupgrade/ajax-upgradetab.php call this url on click upgrade

but its display 

Status Code:

503 Service Unavailable 

and nothing happen ,no updating process start

please help me for fix this issue