how to alter P_K

i have more than 50 tables in sqlserver so everything has connected to each other with foriegn key

so right now the primary key has like 1,2,3,4,5,etc it's auto incriment so this DB am using has server so i have know that there is only one primary key

so the server has only one main primary key

so the main primary key has connected with different tables

so i want to change this primary key like staring point at :8 and autoincriment and incriment seed like 6

like my PK 8,14,20,26,32 like that i want to incriment that primary key

throuhg using QUERY , does anyone knew please...