Click on your username here in this topic while you're still signed into the website and you'll see your synths.
Click on the "x" in the top right hand corner of a synth's thumnail 'card' to delete it.
If you click on your name at the top of the site ("Signed in as mcloveya"), you'll be taken to your profile page. It has four tabs on it:
1: Comments on your Synths (this is where the link at the top right of every page takes you)
2: Replies to your comments on other people's synths
3: Your Synths (This is where you'll go if you click your name in this topic or anywhere else on the site and where you go to delete your own synths.)
4: Your Favorite Synths