Checkout button change

-- url of the page with the problem -- : www.militarycuts.com
-- HikaShop version -- : HikaShop Essential: 2.6.1
-- Joomla version -- : Joomla! 3.4.8 Stable
-- PHP version -- : 5.5.29

Hello.
Just a question, hoe do I change this PayPal checkout button.
it looks pretty bad, very pixelated and the text underneath can not be read.
any help would be appreciated.
merci

Hello,
Note that using some CSS code to edit it will probably do the job :
hikashop.com/support/support/documentati...the-display.html#css
Or edit the "paypalexpress.php" file of the PayPal express payment method and change that ligne :

$this->button = '<div id="paypal_express_button" style="width:144px; height:46px; margin-top:15px;"><a href="'.$notif.'&setExpressCheckout=1"><img src="https://fpdbs.paypal.com/dynamicimageweb?cmd=_dynamic-image&buttontype=ecshortcut&locale='.str_replace('-','_',$lang->get('tag')).'" align="left"></a></div>';

where exatly can I find this file, cause I looked for the last few hours and can't seem to find it.