I have two domains, webhosted on 000webhost. I installed wordpress on them and for some days it functioned well, but now it shows me the following error on both of them: >
Changing the memory limit only hides the problem, it doesn't solve it.
You currently have 64MB of memory, which should be more than enough for your needs. If it's not, then there's almost certainly a leak in your code, or possibly an infinite loop.
Instead of trying to hide the error in a corner, try fixing it. Look at where the error happens, see if you can find what the "last straw" is that makes it exceed the memory limit.