How can i convince my boyfriend that circumcision is wrong?

You can't: Your boyfriend is entitled to his own opinions, especially as regards his body. Circumcision is not necessary, but is still widely practiced.

Tell you prefer not: Depends upon why he wants to be circumcised. A freely retractile foreskin poses no problems and is easily cleaned. If so, tell him that you like him the way he is and that sex may be more pleasureable for both if he remains uncircumcised. Support his decision if foreskin is tight, causing pain or discomfort. Frenum can be divided without circ, if this is tight and cause of discomfort.