Hey Julie,

You can change the logo size by doing changes in email templates.
For this you need to do changes in this file : root\components\com_payplans\themes\wireframe\emails\template.php

Nearline no. 97, find the below-mentioned code.

<img height="auto" src="<?php echo PP::getCompanyLogo();?>" style="border:0;display:block;outline:none;text-decoration:none;height:auto;width:100%;font-size:13px;">

In this code you need to update the height and width in style as per your need and removed height="auto".

Let me know if you will have any queries.