You can change any fund and as often as you want for the 401K account. You don’t need to pay any tax for the capital gain now. However, the transcations have to be in the same account. You can’t move money from one 401K account to different 401K account.
Some people have 2 different 401K accounts since they worked for different company before. Ususally, if you leave the company, you can roll over your 401K money from your old company to the new company.
