I don't know what your level of skill or budget are, or what sorts of changes you want to make? But if you want to go more modern and have the skill, the first thing I'd want to do is change out that light (and possibly the faucet). Something like:

Sun and Stars Lighting 2-Light Energy Efficient GU24 Satin Nickel Bath Vanity · More Info

or

Gemini Crystal Two-Light Bath Fixture · More Info

Aside from that...painting to a better, cooler white or other color is a good idea. I'd paint the trim, too, and the door--the brown (it looks brown on my monitor) wood feels old-fashioned to me. What color were you thinking of for the vanity? Would you do the trim in the same color?

Maybe a stripe around the top of the room, at the same level and thickness as the air vent? Navy or charcoal against the white wall (or whatever color you were thinking of)?

I've painted several of my tile floors, using a good primer and a porch & floor paint, and gotten good results. Dark floors look very modern these days, and I've also seen people stencil their floors to look like those concrete tiles and such, or painted them in stripes.

Maybe a few floating shelves above the toilet?

If you can share some of your taste, colors you were thinking of, and what kind of DIY you have in mind (like, do you mean painting, or do you mean building a whole new vanity?), we'd probably have more suggestions for you.

I hope that's some help, though!

Changing the color of the vanity top would help a lot. It seems to clash with the warmer tones in the room. But I also think that the mirror is part of what is making the room look heavy. I would get a thin framed mirror in place of the one you currently have. You might find that the espresso vanity isn't as heavy-looking at that point.

Walls the same color as the vanity.

SO helpful!! Thank you 🙏🏼 😍 even though it’s not my dream decor, I just want something to make it not feel so dated but with the least amount of changes and $$ I have to put into it. This is like the exact layout of my bathroom so it really is such a big help to be able to visualize what we could transform it into. I will definitely be using this as a guide for our changes! Thank you thank you thank you!!!