This depend son what you want to do: manually via an app, or programatically - the two are different.
Via an app:
Open it in your new, shiny image editing program (or Paint, if that's what you have available)
Use "Save as" (often hotkeyed to F12) and select TIFF as the output format.
Give it a new name and save it.
Programatically:
Depend on the language exactly how to do it, but it's the same process: read it, and save it as a new file. For C#:
using (Image im = Image.FromFile(@"D:\Test Data\Old-style-jpeg-compression.tif"))
{
im.Save(@"D:\Test Data\New-style-jpeg-compresion.tif", ImageFormat.Tiff);
}