This question already has an answer here:
Perhaps this question should have been asked on ELL, but I will try here and move there if fail here.
There are verbs (currently I've found rest, walk and another one I'd better not cite) which can be used also with a verb have (and take) and respective noun (e.g. rest - have a rest etc). So basically what is the difference here:
rest - have a rest, take a rest
walk - have a walk