You can clear your phones cache by doing the following:
1. Go to your phones settings
2. Tap Storage
3. Tap Cached Data
4. It will confirm you want to remove cached data.

To uninstall apps you don't use from Google Play:
1. Open the Menu.
2. Click Settings
3. Select Applications.
4. Click Manage.
5. Select the app you want to uninstall, then click the Uninstall button.