IF condition in Text field

Hi there, 

I have a [B!T Client Rating] Text field, it can contain numbers 1 to 5 or it can contain stars, so *, **, ***, ****, or *****. So I want to unify and convert the stars to numbers. I created a Formula text field and I put the following:

if([B!T Client Rating] = "*",1, [B!T Client Rating])
if([B!T Client Rating] = "**",2, [B!T Client Rating])
if([B!T Client Rating] = "***",3, [B!T Client Rating])
if([B!T Client Rating] = "****",4, [B!T Client Rating])
if([B!T Client Rating] = "*****",5, [B!T Client Rating])

It doesn't like the = in the first line. It says: "The operator "=" can't be applied on type numbers, text".

Any ideas? Thanks!!