Translating use case to class diagram

I would appreciate any help/advice on this. I have a project to do for uni and it entails creating an app that will sync a file/directory across the network to a server/the cloud. I have completed my use case diagrams but i am having some trouble translating those into class diagrams and in particular fitting in the “sync contents” use case.

These are my class diagram so far but I dont know where i should include the sync contents class or what/how it should be related to.

I am new to UML and OOP so any pointers would be useful.Thanks in advance.