>Hi All, my app (Winforms) consists of an exe and several dlls, is it possible to make some changes to just one assembly and redeploy it ( the dll )? or do I have to update everything ?

Depends. <s>

Obviously if you've made a breaking change to the assemblies interface the answer is no <s>...

Also if you're signing your assemblies and you're changing version numbers any calling assembly must be recompiled to see the right version of the assembly. But non-signed assemblies don't use the version numbers for assembly binding.