Partial PUT is a dangerous thing, as you don't know the state of the resource you are updating, so leading to improper replacements. There are two ways of solving the issue:
* define a PATCH method, unlike the PUT, the format associated with PATCH containsa instructions on how to express the difference between the original version and the new one that the server can verify to ensure the PATCH is done on the right data.
* Versioning, not unlike the use of ETags in HTTP, to ensure that actions are performed only when the right version of the resource will be modified by the server.