Ways to speed up Code Execution - VBA - excel

Question

I have code that runs and does what I want it to do with the click of the command button, however when executing, it runs very slow. The code grabs data from one sheet and inserts/formats it into another sheet in two separate tables that have been converted into range. I did this because I need to automatically update two different graphs with certain data. I'm still new with VBA coding and any kind of direction or help to make the code run faster is appreciated, whether that be tips or ways to get rid of unnecessary code since it is probably longer than it needs to be.
Public Sub Button1_Click() ' Update Button
Application.DisplayAlerts = False
Application.ScreenUpdating = False
Dim lastRowPart As Long
Dim lastRowCW As Long
Dim lastRowQty As Long
Dim lastRowQtyLeft As Long
Dim lastRowDescrip As Long
Dim i, j, k As Integer
Dim IO As Worksheet: Set IO = Sheets("Inventory Overview")
Dim TD As Worksheet: Set TD = Sheets("Trend Data")
'1. Copies and formats data
lastRowPart = IO.Cells(Rows.count, "F").End(xlUp).Row
lastRowDescrip = IO.Cells(Rows.count, "G").End(xlUp).Row
lastRowQtyLeft = IO.Cells(Rows.count, "O").End(xlUp).Row
lastRowQty = IO.Cells(Rows.count, "I").End(xlUp).Row
lastRowCW = IO.Cells(Rows.count, "L").End(xlUp).Row
TD.Cells.UnMerge ' reset***
j = 2
k = 2
For i = 2 To lastRowCW
If IO.Cells(i, "L").Value = "Unknown" Then
TD.Cells(j, "G").Value = IO.Cells(i, "L").Value
TD.Cells(j, "H").Value = IO.Cells(i, "F").Value
TD.Cells(j, "I").Value = IO.Cells(i, "I").Value
TD.Cells(j, "J").Value = IO.Cells(i, "O").Value
TD.Cells(j, "K").Value = IO.Cells(i, "G").Value
j = j + 1
Else
TD.Cells(k, "A").Value = IO.Cells(i, "L").Value
TD.Cells(k, "B").Value = IO.Cells(i, "F").Value
TD.Cells(k, "C").Value = IO.Cells(i, "I").Value
TD.Cells(k, "D").Value = IO.Cells(i, "O").Value
TD.Cells(k, "E").Value = IO.Cells(i, "G").Value
k = k + 1
End If
Next
' Autofit
TD.range("B1:B" & lastRowPart).Columns.AutoFit
TD.range("E1:E" & lastRowDescrip).Columns.AutoFit
TD.range("H1:H" & lastRowPart).Columns.AutoFit
TD.range("K1:K" & lastRowDescrip).Columns.AutoFit
'2. Sort Cells
Dim LastRow As Long
LastRow = TD.Cells(Rows.count, 5).End(xlUp).Row
With TD.Sort ' sorts data from A to Z
.SetRange TD.range("A2:E" & LastRow)
.Header = xlGuess
.MatchCase = False
.Orientation = xlTopToBottom
.SortMethod = xlPinYin
.Apply
End With
'3. Merge CW Cells
' rngMerge = range for parts reworked/left with known CW
' URngMerge = range for parts reported with unknown CW
Dim rngMerge As range, URngMerge As range, cell As range, lastRowMerge As Long, ULastRowMerge As Long
lastRowMerge = TD.Cells(Rows.count, 1).End(xlUp).Row
ULastRowMerge = TD.Cells(Rows.count, 7).End(xlUp).Row
Set rngMerge = TD.range("A1:A" & lastRowMerge)
Set URngMerge = TD.range("G1:G" & ULastRowMerge)
MergeAgain:
For Each cell In rngMerge
If cell.Value = cell.Offset(1, 0).Value And IsEmpty(cell) = False Then
range(cell, cell.Offset(1, 0)).Merge
GoTo MergeAgain
End If
Next
MergeAgain2:
For Each cell In URngMerge
If cell.Value = cell.Offset(1, 0).Value And IsEmpty(cell) = False Then
range(cell, cell.Offset(1, 0)).Merge
GoTo MergeAgain2
End If
Next
Application.DisplayAlerts = True
Application.ScreenUpdating = True
End Sub