You have a couple of options:
1) Take an UPTOWN #1, 2 or 3 train to 42nd St Times Square (one stop) and walk over to 6th Av/42nd St (Bryant Park)
2) From Penn Station, exit at the 7th Av side, walk over to 6th Av/Broadway and take an UPTOWN B, D, F or V train to 42nd St-Bryant Park (one stop)
1) Take an UPTOWN #1, 2 or 3 train to 42nd St Times Square (one stop) and walk over to 6th Av/42nd St (Bryant Park)
2) From Penn Station, exit at the 7th Av side, walk over to 6th Av/Broadway and take an UPTOWN B, D, F or V train to 42nd St-Bryant Park (one stop)