Drop Table when it references by Other table

hello sir,

I have two Table Branch_Master (Branch_No(pk),Name) and Emp_Master( Emp_No(pk),  FName,MName,LName,Dept,Desig,Branch_No(FK) Branch_Master)  

 1) how can i  Alter the column Branch_No.

2)how can i Drop The Both Tables.

 

Thank You.