If it turns out to be 78 put it on your computer hard drive and get a free software called "Audacity" to edit it to the proper speed. "Audacity" is a fantastic bit of software. I used it to transpose vocal accompaniment for a solo at church and it worked perfectly without changing the speed of the recording. And it is FREE!!
It all depends on the speed intended by the recording itself. Right now, I am listening to Cynic's "Carbon-Based Anatomy" EP on a 10-inch vinyl. The label on the disc says to play it at 45 and it sounds awesome. If your record doesn't tell you, then you're just going to have to experiment with speeds and hope that it's not intended to be 78.
Just to expand, I've got few 10"s that play at 45 rpm. One of them, a 1-sided press, also came on a 2-sided 7" and a double-sided (yup, same thing on both sides. WTF?) 12", all play at 45 rpm. 9 songs, 3 sizes, 10:40 approx. total run time. I've also got a two 7"s that play at 33 1/3 with 14 and 16 tracks. Do you call them EPs? LPs? 45s? 33s? Size and speed aren't necessarily mutually exclusive. Next we'll discuss shaped discs LOL
As Wesley said, you can manually set the needle to a 10" record, but this turntable doesn't have a setting for 78 RPM so it will not properly play those discs. As lots of 78s came in the 10" size you'll want to be cognizant of this limitation as you assess your record collection to see if this is the right player for you.
In the 80s, record labels issued what were called "nu discs", 10" 33-1/3 records with four to six tracks each, mostly by "new wave" bands. I had the nu disc of Gary Glitter, Oingo Boingo's original 4-track Ep and even the Police album "Regatta De Blanc" pressed on two 10" discs.
As for the 78s, I have most of them on cds, so I would only play them on my 1930 Victor Consolette Victrola, anyway.