Let me try to explain it, Aquí and Allí are really similar to Acá and Allá the main difference between them is the "Imaginary distance", how is this? well, Aquí and Allí are more specific than the others, for example : If I am saying : " Aquí en Venezuela tenemos muchos problemas" ( Here in Venezuela we have a lot of problems), I am telling you that specifically in Venezuela we have problems, we also can say Acá en Venezuela but Acá is communly used when we talk in general, like If I say Acá somos buenas personas (Here we are good people) but in that case I am not being specific so you can understand Acá en Venezuela, Acá en Sudamérica (South America), Acá en América, ok?, and also Acá is used to finish a question as "Vienes para acá?" ( Are you coming here), but you can´t say "vienes para aqui?"
Allá y Allí is almost the same thing, in this situation Alli would be like Aqui, and Allá like Acá but let´s say is the same method, Allí is more specific, and Allá more general, and when you finish a question then you need to use Allá, like "Vas para allá?" instead of Vas para alli?
I hope I was clear, If you don´t understand,need practice or more information , don´t be afraid to contact me, have a nice day =)