How do I take ownership over something willed to my brother?

Every state has its own rules about ownership and wills, and in part this depends on whether or not you have to probate your dad's estate. In some states there is a minimum threshold for having to process the will through the court process, and if the total assets are below that threshold you only have to prepare a written declaration about the assets and the will.

It also depends on what your dad said in his will about this car. If he said who should inherit it then that is what you should do; if he did not specifically mention it then it would be considered part of the "residual" estate and that would pass to whomever he listed as his residual heirs. Even if you are an executor that does not mean you can take anything for yourself; your duty it to carry out the terms of the will.

Once you figure out whether you have to take this through probate and who is the rightful heir to the car, you will need to change the title at the state vehicles office. Again, every state has its own rules for making this kind of transfer, and you should check with your local vehicle registration office to learn how this is done. They will probably require some kind of probate court order or maybe a declaration from you and your brother.