WebERP Not working properly after my server migrated from PHP 5.6.x to PHP 7.0.x

[newuser990]

I have WebERP 4.12.3 version installed and it was working fine till recently.
After my web-hosting service provider's server recently upgraded to newer version of PHP (Migrated from PHP 5.6.x to PHP 7.0.x ) I have been receiving error messages as below :

Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; PurchOrder has a deprecated constructor in /home4/xxx/includes/DefinePOClass.php on line 7

Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; LineDetails has a deprecated constructor in /home4/xxx/includes/DefinePOClass.php on line 207

Apart from this, I am not able to generate PDF files of Purchase Orders etc. and I get an error

Warning: Cannot modify header information - headers already sent by (output started at /home4/xxx/includes/DefinePOClass.php:7) in /home4/xxx/includes/tcpdf/tcpdf.php on line 7693
TCPDF ERROR: Some data has already been output to browser, can't send PDF file

Please help me out.