Uppercase to lowercase with JE condition

.model small
.data

msg1 db 'Enter a letter: $'
msg2 db 'Letter in lowercase: $'
msg3 db 'Enter a number: $'


A db ?
B db ?

.code
main proc
    mov ax, @data
    mov ds, ax

    lea dx,msg3
    mov ah, 9       ;Print String
    int 21h

    mov ah,1
    int 21h

    mov A, al
    int 21h

    mov ah, 2
    mov dl, 0ah ;new line
    int 21h
    mov dl, 0dh ;remove space
    int 21h

    CMP A, 53       ; CMP=Compare, JE=Jump Equal
    JE l1           ;Goto l1

    JMP exit        ; JMP=Jump Goto Exit

    l1:
    mov ah, 9
    lea dx,msg1
    int 21h


    mov ah,1
    int 21h

    mov B, al
    add B, 32       ;Math
    int 21h

    mov ah, 2
    mov dl, 0ah ;new line
    int 21h
    mov dl, 0dh ;remove space
    int 21h


    mov ah, 9
    lea dx,msg2
    int 21h

    mov ah, 2
    mov dl,B
    int 21h


         exit:
         main endp
end main