To try and address your 'how' it goes a bit like this.
You need to first assess how your stuff is invested, if for example half is in stocks, and the other half is in bonds, then you will need to calculate a 'blended' rate for what are reasonable 'average return' for both. That might mean looking at the S&P500 or Russell 3000 for the stock portion, and some bond index for that portion, then 'blend the rates', in this case using a formula like this
(R3000_return * .5) + (bond_return * .5) = blended rate
then compare the blended rate with the return in your IRA.
It is generally a lot more useful to compare the various components of your total return separately, especially if you investing with a particular style such as 'agressive growth' or you are buying actual bonds and not a bond fund since most of the bond oriented indexes are for bond funds, which you can't really compare well with buying and holding bonds to maturity.
Lets say your stock side was two mutual funds with different styles, one 'large cap' the other 'aggressive growth'. In that case you might want to compare each one of those funds with an appropriate index such as those provided by Morningstar If you find one of them is consistently below the average, you might want to consider finding an alternative fund who's manager has a better track record (bearing in mind that "past performance....")
For me (maybe someone has a good suggestion here) bonds are the hard thing to judge. The normal goal of actually owning bonds (as opposed to a fund) is to retain the entire principal value because there's no principal fluctuation if you hold the bond to maturity (as long as you choose well and the issuer doesn't default) The actual value 'right now' of a bond (as in selling before maturity) and bond funds, goes up and down in an inverse relationship with interest rates. That means the indexes for such things also go up and down a lot, so it's very hard to compare them to a bond you intend to hold to maturity.
Also, for such a bond, there's not a lot of point to 'switch out' unless you are worried about the issuer defaulting. If rates are up from what you are getting on your bonds, then you'll have to sell your bond at a discount, and all that happens is you'll end up holding a different bond that is worth less, but has higher interest (basically the net return is likely to be pretty much the same). The better approach there is generally to 'ladder' your maturity dates so you get opportunities to reinvest at whatever the prevailing rates are, without having to sell at a discount.. anyway the point is that I'm not sure there's a lot of value to comparing return on the bond portion of an IRA unless it's invested in bond funds (which a lot of people wanting to preserve principal tend to avoid)