What is the best way to make this wall straight

[Kurtis001]

Hi all this is my first post. I have just brought this house and our basement is a great space to turn into a second living room. I know how to sort the floor but I don't know what is best for the wall.

Plaster it or batten it...

If batten how would I be able to make it straight ?

Any help you can offer would be great.

 

[He who knows]

What is the best way to make this wall straight

If batten how would I be able to make it straight ?

It's not clear from the photos in what way, and by how much, it is out of true.