How to change the donation values in Donate Now popup box?

you can change values either globally or in individual cause :)

1 : for global :

go to WP-admin-panel > charity hub > cause style and in donation form field you can specify values like this :

[gdlr_paypal user="[email protected]" val_1="100" ,  val_2="75" ,  val_3="50"]

2 : to change values in individual cause : edit your cause and do same as above in cause's donation form field .

Cheers !