That could be tricky
I don't know of any way of combining partitions without losing anything, aside from making a complete backup copy of them onto another partition, combining them, and then restoring from the backup.
Is there a special reason they need to be combined into a single partition? You can reformat your Windows partition as ext2 and just mount it wherever it would be convenient (after backing up anything you need to keep first). Having multiple partitions is actually safer than having single large partitions, since if something goes wrong with the filesystem, you don't lose everything; you just lose one partition. Unless you really need a single partition, I'd recommend just leaving it separate.