I ended up following equipment:

Shimano Tiagra FH-RS400 rear hub
Shimano Altus Cs-Hg31-8 11-34T rear cog
Shimano CN-HG40 6/7/8 Speed Chain
Shimano Altus RD-M310 rear derailleur 6/7/8S
Shımano Altus SL-M315 Shifter 8S
Shimano Acera V-Brake front and back

After that I also needed to replace front hub with one which is 113mm length. Previous was 122mm length. I changed it because the chain was coming off the front cog when İ changed the gear from two to one on hills.

Now it goes faster and easier to climb hills.

Thank you all for helps and opinions.