Howdy, Robert! Welcome to planDisney and thanks for your question!
You can most certainly change your
theme park reservation to a different day. In order to do so, you will need to cancel your current reservation and make a new one. So I highly recommend checking the
theme park reservation availability calendar before making new plans. Additionally, if you have a one-day ticket, it likely belongs to a specific ticket tier. To see which days certain ticket tiers are valid, view this
FAQ page.
If you have a one park per day ticket, the other option would be to upgrade it to a Park Hopper ticket. This way, you can still enjoy Disneyland Park on February 10th, but then hop over to Disney California Adventure Park in the evening when Disneyland Park closes for Sweethearts Night. To upgrade your ticket, simply stop by a ticket booth.
I hope you have a great time at the Happiest Place on Earth!
-Linda