Finally found a tower defense game!
Nice concept, and nice job on it. I did find it hard to modify my towers at times. If you continue to tinker with it, it would be nice if the menu on the right showed you what was available for the fighter on the board instead of having to click them from the top, especially if you can't afford to add a different type of tower. I could click the upgrade button from the character on the field, but I couldn't easily change their weapons unless I could afford to click on one of the new towers to buy (meaning I couldn't even see what I could equip for, say, the mage if all I could afford was the knight - I only saw the knight weapons).
It would also be nice to add some sound effects during combat, though you may have run into issues like my game has where a lot of things happening at once can make it really loud (or you may have had other reasons not to add those sounds, of course). I learned a few ways to handle multiple sounds at once after I posted my game, like running a code to check for X actions happening within the same Y moments and basically telling it to only play so many of those sounds so they don't overlap. A few people gave me advice on it, so if that happens to be something you were trying to figure out, I definitely recommend checking out the dev channels in the discord and posting about it.
Anyway, really nice entry, and I was in the mood for a tower defense today, so it was great to play it!