it is typical for tomato plants to lose the bottom (oldest) leaves after awhile. Yours don't look too bad. I would remove them anyway. If it spreads to newer leaves or if you get more spotting, you may have some fungal disease like septoria leaf spot.
Tomatoes are very prone to this.
Here's one of our threads about septoria: https://www.helpfulgardener.com/forum/vi ... ia#p389156