I Need A Sp That Will Update A Field Based On Conditions

I need to update the status of a client when they make a payment of a certine amount. My problem is this, the two pieces of information needed to do this are comming from two tables. For example;

@ClientID Int,

@PmtAmt Money

IF @PmtAmt >= tblSettings.TopAmt THEN

Update tblClients

SET

ClientStatus='High'

WHERE ClientID=@ClientID

ELSE

Update tblClients

SET

ClientStatus='Medium'

WHERE ClientID=@ClientID

ENDIF

How do I do this in a stored procedure? I need to select the TopAmt from the table tblSettings and then update the table tblClients.