I came up with an idea to solve a major problem but Theres was already a patent out. But it was patented back in the 40s and have since expired. But i see similar patents which are newer. I am not to sure if they all have changes " it's a lot and im to lazy to go over every detail "the original is really all i need to copy so can i legally use it or is there a change the other patent holders already repatents it?
The basic requirements for a patent is that the idea be useful, novel and non-obvious. If someone has already patented an idea, then you can't re-patent it because it would not be novel since someone else already thought of it. This goes to the fundamental deal with patents. In return to teaching the world about your idea, you get a limited period of exclusivity. Once that limited period is up, anyone can use the idea.
You mention other related patents. It is very common for people to invent improvements to existing technologies. You do need to understand what those improvements are as they relate to the product you intend to sell. If you search for the original patent on https://patents.google.com you will see a section on the right side of the page that looks something like this.
The "Cited by" link will take you to patents that cite this patent as prior art. This is a good place to start to look for newer, related patents. You don't need to read each and every word of the related patents. Mostly you need to focus on the claims, especially the independent claims (claims that don't refer to other claims). It takes some practice to read claims, but you need to understand whether a non-expired patent exists that impacts your product. Patents now expire 20 years from the filing or priority date which ever is earlier so any patent from before 1997 is probably expired by now.