If you're referring to the spacing left and right of Σ, it is there so that the summation criteria you've written can be displayed. Perhaps this?

"" <= sum from{binom{[x_{i-1},x_{i}]}{ " " subset K} } %epsilon %DELTA x_i +

sum from{binom{[x_{i-1},x_{i}]}{"="[u_j,v_j]} } 2M %DELTA x_i <= %epsilon (b-a) +

2M sum(v_j - u_j) underbrace{""<%epsilon} <= %epsilon(b-a+2M)

If not, how would you propose to display the summations without this spacing, while showing the criteria?

If this answered your question please go to your first post use the Edit button and add [Solved] to the start of the title. You can select the green checkmark icon at the same time.
Mr. Programmer

AOO 4.1.5 Build 9789 on MacOS 10.11.6. The locale for any menus or Calc formulas in my posts is English (USA).