The easiest way this can be done is if you have access to their login information. Then you can just log into their account, go into settings, then account and delete the account.  

If you don’t have their login info it can be a little harder but most social media platforms have a form you submit. Many of them need one of the following documents for proof:

-Birth certificate (in cases where the deceased is a minor).

-Last will and testament

-Estate letter

-Obituary

-Memorial card

-Power of Attorney 

-Executive Order

Here are the links to common platforms:

Facebook: https://www.facebook.com/help/1518259735093203

Managing the account for memorialization-

https://www.facebook.com/help/1506822589577997

Instagram: https://help.instagram.com/151636988358045

Snapchat: https://help.snapchat.com/hc/en-us/requests/new

Linkin: https://www.linkedin.com/help/linkedin/ask/TS-RDMLP?lang=en&lipi=urn%3Ali%3Apage%3Ad_flagship3_pulse_read%3BCSuR53hmTMekN%2FxbhJ4P3Q%3D%3D 

Pinterest: Email care@pinterest.com with the deceased user’s details, including their account username, the obituary of the deceased, and proof of your relationship to the deceased: https://help.pinterest.com/en/article/deactivate-or-close-your-account 

Tiktok: contact TikTok at feedback@tiktok.com

Twitter: https://help.twitter.com/en/rules-and-policies/contact-twitter-about-a-deceased-family-members-account 

Youtube: https://support.google.com/accounts/troubleshooter/6357590?hl=en