How to change tubes ??? (NEWBIE)

[leimaster]

Hi to everybody.
I have a Music angel with n°2 12AU7, n°2 12AT7WA and n°4 KT88.
I would like to change the first two kind (I have them from Mullard), but I don't know if something can be broken.
Reading the other posts I saw something about the bias. There is a bias for this kinds of tubes too?
Bye

 

[SHiFTY]

Turn the amp off, and pull out the old, plug in the new and play. Small signal tubes (12AU7 etc) are autobias and do not need adjustment.