Call a structural engineer to provide you with the solution and then decide if the job is within your skill set. If you own the right tools, it should be. It's not that complex. It's mostly just muscle and tools. If you decide to hire a contractor to do the job, then you will already understand what needs to be done and will be better able to evaluate their bids for the job.

The biggest issue is how you provide a header for the new wider opening, while maintaining support during construction.

Do you have enough height in the wall for the door you want and the new header?

If there is not enough height for a wood header you may need to use a section of steel for the header.

Cutting through block is not that hard until you run into grouting and re-bar in the block.
Then is gets harder to deal with and maintain the load bearing capacity and strength of the wall.