How to transfer 1040SR to 1040 when taxes finished?

It is not possible to transfer the 1040SR to form 1040.  I question why you would need to do this, since the forms contain the same information.

how about if I prefer to use 1040 instaed of 1040sr

If you were 65 or older at the end of 2019 you will automatically get form 1040 SR. There is no extra fee for using form 1040 SR and it is the same as Form 1040 with bigger print.