Level 67
I guess it depends on how complex your app is and what you've done. Spark recommends to be installed on a new project (not existing) since it uses custom auth controllers, user/team models and some other things that could mess up an existing app.
I'd start with a fresh install of spark, get it set up and working on it's own, then start copying your code over and merging things where appropriate (like user class, etc)