The major change in the fork is an increased block size. As you know, transactions on blockchain are recorded in blocks, that are periodically appended to an existing chain. Larger the block size, the more transactions it can hold, so more people are able to transact using the cryptocurrency in a fixed amount of time. The block size in Bitcoin Cash will increase four times, from 8MB to 32MB.
One of the main criticisms against Bitcoin is its lack of scalability. Put in simple terms, Bitcoin is not able to meet an increased demand and people who want to transact with it often have to wait hours or days. This undermines a main functionality of Bitcoin as a currency, being a medium of exchange. It was the main motivation behind the creation of Bitcoin Cash, which has a larger block size. Still, today, Bitcoin Cash can only process about 60 transactions per second, much less than what other payment services can offer. Visa can handle up to 2000 transactions per second, PayPal – 185 and Ethereum – 100.