Google the brand of the wall mount. It's on the black sticker in the middle. It will let you know what size tv it can hold. Personally I would remove it and buy a new one that fits the tv size and works with placement I want.

That looks like a rail style. I don't think you can buy the VESA mount separate anyway. Rails may be for a much larger tv than 42" class too, so may not be mounted at a height for an appropriate viewing angle for a 42" class. For the larger mounts, usually they come with lag bolts, those screws may not be instructions-compatible. Start fresh.

Thank you!!