You know I was thinking about this when I was talking with my friend about which blood types we were. I'm O+ and if someone gave me A or B, would mine change over?
No.
No, and you'd get seriously ill, possibly fatally.
Quite - Blood received in a transfusion must be compatible - have the same antigens as yours (A,B,O and Rh factor). If you get a transfusion of incompatible blood (different antigens), the antibodies in your plasma will destroy the donor blood cells. This is a transfusion reaction. The reaction can be anywhwere between mild and fatal.
O neg blood does not have any (major) antigens and is compatible with any blood type (universal donor, can be tranfused to anyone without reaction). Type AB pos blood can receive blood of any type (universal recipient). The major antigens aren't the only things that need matching and the universal donor / recipient matching is only used in emergencies.
Women with Rh negative blood types need to be careful with pregnancy - if the developing baby has Rh positive blood the mother's immune system can start producing antibodies that
may destroy the developing fetus's red blood cells. Note: Rarely a problem on a first pregnancy as the antibodies form 'too late' to have a negative effect, but subsequent pregnancies need to be monitored and, if necessary, treatment administered.