editing pay button

I am using paymill for wordpress and want to change a couple of things but don’t know how, I am not a programmer and have limited knowledge.
the webpage is http://www.svgplaydays.co.uk/buy-a-voucher

Firstly the dropdown box to select quantity only has ‘0’
Second next to the dropdown box and before the price is an ‘a with dash above’ how can I delete this.
Thirdly can I change ‘zip code’ to ‘postcode’

At the moment I am using the shortcode to call the script

https://wordpress.org/plugins/paymill/