Is it necessary to show what improvements you have made to similar work in literature reviews section?
Contrasting your work with earlier work on the same topic (same or related questions) is a crucial part of a scientific publication. You have to explain to the reader what makes your approach better (or worse) depending on the exact problem to solve.

Now, whether you should do this in the section devoted to review of the existing literature is debatable. There are no strict rules, so as long as you do it somewhere and the paper is clearly readable, just do what seems best to you. If you have trouble writing, I would suggest you separate the content into a simpler form:


State of the art: review of the existing literature. What problems are solved, what are remaining questions, where can we make progress. This is the motivation of your work.
Your methodology
Your results
Discussion of how these results compare to earlier work: you're doing better than A and B on large matrices, but the approach means that you will be slower than C on sparse matrices, that sort of stuff.