Explode and update data in a field using mysql

Explode and update data in a field using mysql

I've got a varchar field with data like this
1 2 3 4 5 6
And i need to add "5" to the first two numbers into that field (1 and 2)
So the result should be
6 7 3 4 5 6
I can't change the way the data it's stored...
Thanks in advance