Church Names and St Oswald

For some time now I have been trying to find out how churches were given their names. I have searched the internet and even contacted the library at Lincoln Cathedral, all to no avail. For example why was Blankney Church named St Oswald's and who decided that was the name it should have. I am sure there must be an organised and meaningful method of allocating names to churches but what is it and who decides. I presume that St Oswald's has always been the name of Blankney Church. The present church is said to date back to the 11th century but was rebuilt on the site of an earlier church. Was the earlier church called St Oswalds? If anyone can tell me why,or when, it was called St Oswald's please let me know. I would be very interested to find out. To take it a step further what do we know about St Oswald, probably known as Ossie to his friends. He was born in 604, the son of Ethelfrith King of Northumbria. At the age of 12 he fled to Scotland, when his father was killed by his uncle Edwin. Obviously not a nice family. Oswald eventually went to St Columba's monastery on the Scottish island of Iona. Following the death of Edwin in 633 Oswald returned to Northumbria as king. St Aiden another of St Columba's disciples was asked, by Oswald, to found a new monastery at Lindisfarne off the coast of Northumbria. From there christianity was to be spread throughout Oswald's kingdom.
At the battle of Maserfeld near Oswestry Oswald was killed by King Pendra of Mercia in 642.
Oswald's body was dismembered but his head was recovered and sent to the monastery at Lindisfarne. The monks at Lindisfarne were driven out by viking raiders in 875, they carried with them the head of Oswald. A great new monastery was established at Durham by the descendants of the Lindisfarne monks and it was there that the head of St Oswald was eventually buried. It remains there to this day. St Oswald's feast day is 5th August.