If you want to "slay" the vampire, you'll have to start from the computer, then buy vampire tomes (4 in total) and get the vampire lore skill to level 15. After that, your sim can make an ultimate vampire cure. Then find the vampire, make the relationship go down so you can fight him/her and choose
Slay Vampire.
Again, I'm not putting my text tutorials here.
Instead I put a Google search here about vampire lore skill. Find a guide to help you and if you like, you can still find my video that way.Link: https://www.google.ee/search?source=hp&ei=GcBLW7DyHLKJmgXJgKrgAw&q=sims+4+vampire+lore&oq=sims+4+vampire+lore&gs_l=psy-ab.3..0i203k1l3j0j0i22i10i30k1j0i22i30k1l3.982.4502.0.4805.20.14.0.4.4.0.379.1880.0j9j0j2.11.0....0...1c.1.64.psy-ab..5.15.2015.0..35i39k1j0i131k1j0i67k1.0.EY8QMrOMJY8
Edit: Oh, the Google search doesn't work and it takes you to the main page. Just search this:
the sims 4 vampire lore
