How to update from remote origin with local modified branch?

I have once cloned a a project from a remote repository: git cloned http://repo.or.cz/r/openbsc.git

After that I modified some files and commited. In the mean time the remote repository had several commits. Now I want to update my local repo from the remote repo but I also want to keep my own commits. So, when doing "git pull" I get the message that certain files needs to be updated.

Now, how can I get my local repo, with my own modification, updated by the remote repo? I know I need to be aware that those updates (or commits) from remote must not conflict with my local.

Thank you.