There are two reasons why there might be pending transactions shown in the wallet
You reattached a transaction and the reattachment confirmed, making the original transaction pending forever (this does not apply to promotions. Promoted transactions will also confirm the original transaction)
You sent some IOTA (or somebody sent it to you) but the transaction did not confirm and nobody wanted to reattach it.
In the first case, you will see an indentical transaction (with same bundle hash) that is confirmed (also, tangle explorers like thetangle.org will show your original transaction as "reattachment confirmed"). You don't have to do anything with these transactions.
In the second case, there are still pending transactions. In case you are trying to transfer your IOTA now, it could result in a double-spend or in some IOTA remaining (if an incoming transaction gets confirmed later). These transactions will not have a second confirmed transaction with the same bundle hash, and they will show up as "pending" on thetangle.org. You should try to promote/reattach these transactions to get them confirmed before spending your IOTA.
In any case, if you are using a recent version of the official desktop wallet (not the Android one), it will warn you when you try to perform a transaction that may result in a double-spend. So you can try in any case, and just stop if you get a warning.