The 'best' method may depend on a few things like if you have other cells/sheets that have formulas pointing to that original data and such. A few methods include:
a) delete old sheet and rename new sheet with original sheet name (note this will break links/formulas but is quick and easy)
b) on correct sheet select all and copy (or cut), then paste onto original sheet. There IS a difference between copy-paste and cut-paste. If you copy-paste any formula will update based on the relative change but a cut-paste will be treated as a move and try to keep any and all links/references the same.
c) similar to b above you can use copy/cut but choose to paste SPECIAL (go to home and use the down arrow under the paste icon or hit ctrl-alt-v). Then you have options like paste values only, paste format only, or many other options. So again depending on what you need or trying to achieve those option may help.
