@Euskadi750: Following from the screenshot above, you will need to tap the 'Edit' option at the bottom of the screen, then tap the 'View more' drop down arrow below the list of details that appear. For clarity, please follow the steps below.
Open the Phone app > Tap on the Contacts tab > Select a contact > Tap the 'i' symbol > Tap 'Edit' at the bottom of the screen > Tap the 'View more' drop down option > Scroll to the bottom of the list of options > Ringtone > Select your ringtone > Back > Save.
@Euskadi750: Does the issue persist if you access the contact via the Contacts app (swipe up from your Home Screen > Contacts > Select the contact > Tap Edit at the bottom of the screen? If so, you may need to change the storage location of your contacts in order to access the relevant options. To do this, head to the Contacts app > Tap the 3 lines in the top left > Tap the option at the top of the pop up window (above Groups), and make a note of where the contacts are currently stored. If you're not sure, there should be a number next to the relevant category. Now, select Manage contacts > Move contacts, and follow the on screen instructions. I recommend moving them to 'Phone', as this will utilise your internal storage, and should make the options described above available to you once they have been moved. Let me know how you get on.
