Reduce the file size via MACRO

At our dept, we use a file where we track project status and financials. Our usual routine is to dump relevant data daily into a tab from another report than we run a macro that deletes more non-relevant data rows. As we do this daily, the file size increases and I ask the users to follow the steps outlined below. What I would prefer since they are causing many errors as they attempt to do this is to have a macro that would do this automatically for them starting from row 6,001. I tried using create macro function and followed the steps below but it causes errors and it stops working... any ideas?


STEPS
• Find the last cell that contains data in the sheet.
• Delete all the rows after this cell.
• In this example, to delete the rows, select the blank cell after the last cell D11 to the data.
• Select the cell D12.
• Press the key Shift+Space on your keyboard.
• Press Ctrl+****+Down Arrow key.
• Rows will get selected till the last row.
• Press Ctrl+- on the keyboard to delete the blank rows.

I used the 1st option (automatic vs. user) and it gets stuck at: If .Cells(.Rows.Count, i).End(xlUp).Row > LastRow Then

The tab is not protected and I did updated the ColNum and LastRow

Any ideas why?