Select the worksheet
Go to the View tab
Uncheck Gridlines
Select the cells
Go to the Home tab
Open Borders
Choose No Border
Select the sheet
Go to the Page Layout tab
Under Gridlines, uncheck View
If needed, clear conditional formatting borders
Select the range
Go to Home
Open Conditional Formatting
Choose Clear Rules
To remove page break lines
Go to File
Select Options
Click Advanced
Under Display options for this worksheet
Uncheck Show page breaks