Do I need to replace my potting soil?

I remove all old roots and mix in new soil as needed

I amend my soil every spring and everything grows fine. I dump the pots in the fall, the pile freezes over winter to kill anything from the previous summer

I use large pots for growing veggies as well, and I just supplement the current soil each season, as long as the former plants did well and there was not any diseases that harmed the former plants. I also cover my pots in the winter with a make shift cover or lid and that helpls to keep the weeds out during non-use as well as the sun heats up that soil and sort of sterilizes it from any issues. Then in early spring, I add the supplements and mix it all up in advance of planting so everything mixes and blends together. It builds the soil. My plants to just fine.

depends if it is clean, no bugs or fungus etc. from plants or directly in soil. It will help to amend it adding compost,manure or additional new soil. You can add used coffee grounds,crushed egg shells,ground shrimp shells,ground banana peels the finer ground the better if you add them to use now and plant, grind in blender adding water to make slushy then add mix in soil really well. I add Jobes Organic Fertilizer bags to all my potted plants,inside & outside,compost bin and garden beds https://www.google.com/search?q=jobes+organic+fertilizer&sa=X&rlz=1C1CHBF_enUS750US750&tbm=shop&tbs=vw:g&ved=0ahUKEwjpw5iijfPgAhWZJDQIHcP2BSsQvQ0IwgI&biw=1366&bih=657#spd=12755302566188605339

In my bigger flower pots and flower boxes that take so much soil, I have put in empty pop cans, or packing peanuts (the undesolvable kind), or clean plastic butter containers, etc....anything that will not deteriorate and then I put soil on the top. Plants grow, and you can add more soil if you need too. You can fertilize etc. just as if the pot had only soil in it.