You can not delete your own topic. Even if you edit it to del or delete and report it to a moderator for deletion, the moderator will not likely delete it because many people have posted there already. I just saw both topics to be similar and think both topics can be on the same topic and it is nice that you accepted. You can leave it but just in case of next time.
OP can not delete his topics and he only have two options: lock one topic and let it at current board; or move it to Archival board and lock it.
If two topics are similarly and created by a same user, a best option is locking and moving one of two topics to Archival. Forum rules are not allowed duplicate topics too.
12. No duplicate posting in multiple boards (except for re-posting topics in the local language boards if they're translated and re-posting marketplace topics in the altcoin boards if altcoins are accepted).