Reducing the size of your Excel file by deleting blank rows and columns is a great way to optimize your file and make it more manageable. Here's how you can do it:

1. First, make a backup copy of your original file in case anything goes wrong.
2. Open your Excel file and go to the worksheet that you want to clean up.
3. To delete blank rows, click on the row number of the first blank row that you want to delete. For example, if your blank rows start at row 110, click on the number "110" on the left-hand side of the worksheet.
4. Hold down the Shift key and click on the row number of the last blank row that you want to delete. For example, if your last blank row is row 65536, click on the number "65536" while holding down the Shift key.
5. Right-click on one of the selected row numbers and choose "Delete" from the context menu.
6. In the Delete dialog box, choose "Entire row" and click OK.
7. To delete blank columns, click on the column letter of the first blank column that you want to delete. For example, if your blank columns start at column V, click on the letter "V" at the top of the worksheet.
8. Hold down the Shift key and click on the column letter of the last blank column that you want to delete. For example, if your last blank column is column IV, click on the letter "IV" while holding down the Shift key.
9. Right-click on one of the selected column letters and choose "Delete" from the context menu.
10. In the Delete dialog box, choose "Entire column" and click OK.
11. Save your file and check the file size to see if it has been reduced.

If you're still having trouble deleting the blank rows and columns, it's possible that there are hidden rows or columns that you need to unhide first. You can do this by selecting the entire worksheet (click on the box at the top left of the worksheet where the row numbers and column letters meet) and then going to the Home tab and clicking on the Format dropdown. From there, choose "Hide & Unhide" and then "Unhide Rows" or "Unhide Columns" as needed.