Hi,
You are probably going to use the internal OSC if you are using this question. Then you have to pay attantin to the fact that if you are going to use this PIC in a HOT invirument, then your internal OSC will chage.
If not, then ( when using C ) you can write the new code into OSCCAL, and wait 1ms for the OSC to stabalise, or using ASM as CYR wrote.
If you need autoupdate for the OSC when using HOT inviroment, post your request and i will write it down how i did it.
Good luck.