You can clear each app's cache if you do not want to delete applications. Here are the steps to delete the cache for different apps
Step 1: Go to settings.
Step 2: Next to the storage in settings.
Step 3: Select other apps.
In other apps, you will find the list of the app from which you can select the app for which you want to delete the cache. Deleting cache can help you fix your slow down app.