The deeds should be more specific. Normally a right of way is granted because it leads somewhere (e.g. to a garage or parking area), and the right is to pass over the land but not to obstruct it eg by parking on it. This is normally stated in the deeds, &/or in the document which granted the right. There is also a possiblity that other people also have a right of way over the same land, & the owner of the land will certainly have a right to use it in any way which does not breach your right of way.
So you need to do some more investigation to find out exactly what you are allowed to do.
However, if the right of way is just a passage and does not lead anywhere, and if you are not impeding anyone else's use of it by parking there, then in practice you can probably do so. But don't get the idea that you actually have a right to park there. The very fact that it is called a right OF WAY indicates it is a right to pass over the land - nothing more.