How can I decompile from Ex4 to Mq4 (just asking to PROTECT MY EA... I am not gonna do it as it is illegal)

Trading Systems Expert Advisors and Automated Trading
1

I just had a question, If we wanted to modify or change the source code of an expert advisor without having its mq4 file. how can we do ?

I know there are paid services
but i wanna know how can I do ?