Greenlight Capital's David Einhorn has increased his firm's ownership stake in Apple (AAPL) - Get Report , according to a May 16 U.S. Securities and Exchange Commission filing, to 8.21 million shares in the first three months of 2015, up from the 6.28 million shares Greenlight owned in the last three months of 2015.

Despite the big name behind the share purchases, TheStreet's Jim Cramer advised investors to ignore the development, and instead, encouraged them to make up their own mind as to whether Apple should be in their portfolio.

"I've always urged people to pay no attention [to 13-Fs]," said Cramer, TheStreet's founder and manager of the Action Alerts PLUS portfolio, which owns Apple. "Do their own work. If you like Apple and you like the products, you should own the stock." 

"These people [filing the 13-Fs], we never know when they're going to get in or get out. We don't know if they're good, we don't know if they have redemptions," Cramer continued, referring to the possibility of investors returning their shares to Apple.

"There's an -- I would say obsession with it because the public filings come out and people think these [13F filers] are the masters of the universe," Cramer said. "The 13-Fs come out and everybody obsesses over them, and I think they should ignore them."

News that Einhorn upped his fund's stake in Apple comes on the heels of news that Warren Buffett's Berkshire Hathaway (BRK.A) - Get Report had made a $1 billion bet on the Cupertino, Calif.-based technology behemoth. The investment, the Wall Street Journal reported, was made by two of Buffett's potential successors.