Can't delete account
Don't delete your account just to get rid of the data on a Yandex service. You can delete unwanted photos, clear your spam folder, or change the answer to a security question that you have forgotten through the service that stores this data. You can find a solution to your problem in the help section of the corresponding service. They are all listed on the main Help page.
Go to Delete Account on the page containing your personal info to completely delete your account. You'll have to confirm the action with a code sent to your mobile phone or email address.
If you didn't link either the number or the phone number, you will have to answer the security question. If you don't remember this answer, follow the instructions on the I forgot the answer to my security question page.